V 


=  9mj.  s 


^  ^mj.  S.  DEPARTMENT  OF  AGRICULTURE* 

BUREAU  OF  ANIMAL  INDUSTRY.— Bulletin  No/ 7.3. 

D.   E.  SALMON,   D.  V.  M.,   Chief  of  Bureau. 


X  H  K 


BACTERIA  OF  PASTEURIZED  AND  UNPASTEURIZED  MILK 
UNDER  LABORATORY  CONDITIONS. 


BY 


LORE  A.  ROGERS, 
Expert  in  Dairy  Bacteriology ,  Bureau  of  Animal  Industry. 


California 

gional 

cility 


WASHINGTON : 

GOVERNMKNt'  PRIKTING     OFFICE. 

1905. 


LOS  ANQELES 

SEP  23  1952 

GOVT.  PUBS.  ROOM 


ORUAMZATION   OV  Till:    BlKKAl     01     ANIMAL   INDISIKV. 


Chief:  D.  E.  Salmon,  D.  V.  M. 
A».mhn)t<!hief:  A.  I).  Mklvin,  D.  \'.  S. 
Chief  Clerk:  E.  B.  Joneh,  LL.  M.,  M.  IX 

Dairy  IHvigiov:  En.  H.  Webster,  M.  S.,  diicf;  Clahknck  B.  I.a.ve,  W.  S.,  as^iiHtant 
chief. 
Inspection  Division:  A.  M.  Farkington,  B.  S.,  D.  V.  M.,  chief. 
Quarantine  Division:  RiciiARn  W.  Hickman,  Ph.  (i.,  V.  M.  I).,  cliief. 
Editor:  George  Fayette  Thompson,  M.  S. 
Artid:  W.  S.  D.  Haines. 

Animal  Husbandman:  George  M.  Rommel,  B.  S.  A. 
Librarian:  Beatrice  Q.  Obehly. 

LABOKATOKIES. 

Biochemic  Division:  Marion  Dorset,  I\I.  D.,  chief. 

Pathological  Division:  John  R.  JMohler,  A.  M.,  Y.  M.  D.,  chief. 

Zoological  Division:  Hrwtos  H.  Ransom,  B.  Sc.,  A.  M.,  acting  zoologist. 

EXPERIMENT   STATION. 

Sujjerintendent:  E.  C.  Schroeder,  M.  D.  V.;  expert  assistant,  W.  E.  Cotton. 

INSPECTORS   IN   CHARGE. 


Dr.  F.  W.  Ainsworth,  Union  Stock  Yards,  Pitts- 
burg, Pa. 
Dr.  M.  O.  Anderson,  care  Geo.  A.  Hormel  &  Co., 

Austin,  Minn. 
Dr.    Don  C.  Ajer,  Post-Offlce  Building,    South 

Omaha,  Nebr. 
Dr.  G.  S.  Baker,  6th  ^nd  Tow-nsend  sts.,  San  Fran- 

ci.sco,  Cal. 
Dr.  L.  R.  Baker,  South  St.  Joseph,  Mo. 
Dr.  A.  E.  Behnke,  room  432,  Federal  Building, 

Milwaukee,  Wi.s. 
Dr.  .lohn  A.  Bell,  Watertown,  N.  Y. 
Dr.  S.  E.  Bennett,  room  338,  Live  Stock  Exchange 

Building,  Kansas  City,  Kan.s. 
Dr.  E.  L.Bertram,  care  J.  S.  Gllmore,  Davenport, 

Iowa. 
Dr.  Fred  Bniginton,  care  Continental  Packing 

Co.,  Bloomington,  111. 
Dr.  J.  J.  Brougham,  care  Missouri  Stock  Yards, 

St.  Louis,  Mo. 
Dr.  G.  W.  Butler,  care  Drummond  Bros.,  Eau 

Claire,  Wis. 
Dr.  J.  B.  Clancy,  National  Stock  Y'ards,  III. 
Dr.  Lowell  Clarke,  room  320,  Qulncy  Building, 

Denver,  Colo. 
Dr.  .loel  E.  Cloud,  care  the  Agar  Packing  Co., 

Des  Moines,  Iowa. 
Dr.  Charles  Cowie,  Ogdensburg,  N.  Y.      ^ 
Dr.  David  Gumming,  912  Lapeer  ave.,  Port  Huron, 

Mich. 
Dr.  Robert  Darling,  care  Chas.  S.  Hardy,  San 

Diego,  Cal. 
Dr.  E.  T.  Davison,  Rushville.  Nebr. 
Dr.  .1.  F.  Deadman,  Sault  Ste.  Marie,  Mich. 
Mr.  Albert  Dean,  room  328,  Stock  Yard  Station, 

Kansas  City,  Kans. 
Dr.  F.  L.  De  Wolf,  care  Chas.  Wolff  Pftcklng  Co., 

Topeka,  Kans. 


Dr.  Geo.  Ditewig,  care  Union  Stock  Yards,  Cin- 
cinnati, Ohio. 

Dr.  E.  P.  Dowd,  care  White,  Pevey  &  Dexter  Co., 
Worcester,  Mass. 

Dr.  0.  E.  Dyson,  316  Exchange  Building,  Union 
Stock  Yards,  Chicago,  111. 

Dr.  Geo.  C.  Faville,  P.  O.  box  7%,  Norfolk,  Va. 

Dr.  J.  W.  Fink,  care  Swift  6i  Co.,  Harrison  station, 
Newark,  N.  J. 

Dr.  T.  A.  Geddes,  care  U.  S.  ponsul,  London, 
England. 

Dr.  H.  H.  George,  507  Johnson  st.,  Louisville, 
Ky. 

Dr.  W.  H.  Gibbs,  care  Morton-Gregson  Co.,  Ne- 
braska City,  Nebr. 

Dr.  L.  K.  Green,  care  Hammond,  Standish  &  Co., 
Detroit,  Mich. 

Dr.  H.  A.  Hedrick,  215  St.  Paul  St.,  Baltimore,  Md. 

Dr.  O.  B.  Hess,  care  Frye-Bruhn  Co.,  Seattle, 
Wash. 

Mr.  G.  8.  Hickox,  P.  O.  box  1145,  Salt  Lake  Citv, 
Utah. 

Dr.  A.  A.  Holcombe,  Aurora,  111. 

Dr.  U.  G.  Houck,  care  Swift  &  Co.,  Fort  Worth, 
Tex. 

Dr.  W.  E.  Howe,  care  Western  Packing  Co.,  Den- 
ver, Colo. 

Dr.  Julius  Huelson,  care  Jersey  City  Stock  Yards 
Co.,  Jersey  City,  N.J. 

Dr.  F.  AV.  Huntington,  U.  S.  ciistoms  oflice,  G.  T. 
R.  R.  wharf,  Portland,  Me. 

Dr.  Robert  Jay,  care  Jacob  K.  Decker  A  Son, 
Mason  City,  Iowa. 

Dr.  G.  A.  Johnson,  Exchange  Building,  Sioux 
City,  Iowa. 

Dr.  James  Johnston,  care  U.  S.  consulate,  2fi 
Chapel  St.,  Liverpool,  England. 


(Concluded  on  third  page  of  cover.) 


\ 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY— Bulletin   No.  73. 

0.   E.  SALMON,   D.  V.  M..  Chief  of  Bureau. 


THE 


IIAC 


OF  PASTEURIZED  AND  UNPASTEridZED  MILK 
UNDER  LABORATORY  CONDITIONS. 


BY 


LORK   A.   RCKiERS. 
Expert  in  Dairy  Jtacfcriolo^y,  Bureau  of  .In  i  ma  I  Industry. 


WASHIXCnON: 

GOV  K  K  N  M  1    N   I       P  R  I  N   I  INC     <>  I"  V  I  C  F, . 
I  <)0  5  . 


LlHTl^R  OP  TRANSMITTAL. 


U.  S.  Department  of  Aoriculture, 

Bureau  of  Animal  Industry, 
Wa-s/ungton,  D.  C,  Mai/  11,  1905. 
Sir:  I  have  the  honor  to  transmit  herewith  a  inaiuiscript  entitled 
*'Tlie  ba<;teria  of  pasteurized  and  unpasteurized  milk  under  labora- 
tory conditions,"  by  Lore  A.  Rogers,  expert  in  dairy  bacteriology  in 
this  Bureau,  and  to  recommend  its  publication  as  Bulletin  No.  73  of 
the  Bureau  series. 

Respectfully,  D.  E.  Salmon, 

Chief  of  Bureau. 
Hon.  James  Wilson, 

Secretary  (f  Agriculture. 

Dy.— 63. 

2 


CO  XT HX IS 


Page. 


Introduction 

Pasteurization 

l'",x|K>riin«'nts  with  raw  and  i)ast('nri/.('d  niillv 

Influcnci'  of  lactic  bacteria  on  tin-  di'\('lo|)nient  of  peptonizing  hacferia 

( 'onclusions 

Sutniuary 

Biblioj^raphy 


12 

L'S 
.SO 

;50 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/bacteriaofpastOOrogeiala 


TilK  BACTERIA  OF  1\VSTKI  RIZKD  A\l)  rNPASTKnilZKI) 
MILK  UNDER  EAKORATORY  CONDITIONS. 


INTKODUCTION. 


Tho  rapidly  incrojisintf  sizo  of  cities,  with  tho  ro.sultin<^  i-cnioval  of 
ii  hii'ov  })ropoi'tioii  of  tho  coiisunicr.s  from  the  source  of  sup})lies.  has 
necessitated  marked  chani^es  in  tlie  transportation  and  stoi'ao'e  of  vari- 
ous food  products.  This  has  l)een.  with  many  sirtich's  of  food,  a  sim- 
ph'  (juestion,  hut  with  othei's  of  a  moi"e  pcrisliahh'  nature  tlie  ])i-ol)h'ms 
involved  iiave  heen  more  com[)l(\\  and  ditlicult.  This  is  cspcciajiy 
ti'ue  of  milk.  In  this  case  we  have  a  food  in  almost  imi\'ersal  use  that 
is  subject  to  rapid  changes,  atlectino-  riot  oidy  its  ap|)«'arance  and  taste, 
hut  also  its  value  and  vwu  its  safety  as  a  food.  The-^"  dian^'-es  are 
hrouj^ht  about  by  l>acteria  whi«*h  are  normally  picsmt  in  milk,  even 
when  it  is  collected  under  the  best  sanitary  conditions,  and  which  lind 
there  favorat)le  conditions  for  raj)id  nudtij)lication.  Thus  w c  fre- 
([uently  Hnd  that,  as  :i  result  of  this  oi-owth.  in  a  coiupaiati\  ejy  few 
hours  milk  may  b<»come  entirely  untit  for  use. 

In  the  smaller  cities  and  towns  th(>  producer  usually  deli\ers  the 
milk  dii'ectly  to  the  consumer,  and  the  probliMU  of  a  ucxkI  milk  supply 
is  simply  one  of  sanitary  barns  and  !i  ))i'oper  coolino-  iuid  handlinu'  of 
the  milk.  In  the  larj^cr  cil  ies.  howexcr.  the  demand  is  too  <^re:it  foi' 
the  inuuediately  adjacent  country  to  supply,  and  the  pi"(Klucer  is  so  far 
remox cd  from  the  consumer  that  a  middleman  is  neces>ai"y.  A  laiL''c 
proportion  of  the  milk  used  in  the  lai'u'i'i"  citie>  of  this  countiv  i-- 
shi])pe(l  l»y  rail,  a  few  comj)anies  ii>ually  l)uyinL:"  the  milk  fiom  the 
farmers  and  disti*il)utin<.'-  it  from  milk  dep(»t>  in  I  lie  cilie>.  Sonic  df 
the  milk  used  in  Boston  couicn  If"  miles  (').' 

The  spread  of  the  city  of  New  York  into  the  >urroundinL;'  counli\  . 
to»rethei-  with  the  inci-easiuL;-  \aluc  of  land  for  lfu<'k  fanning-,  ha- 
foi'ced  the  daily  farm^  farther  and  fai'ther  aw  a\  .  until  now  milk  for 
use  in  New  \'ork  ( 'ity  i-  collected  aloni^-  the  banks  of  the  St.  Law  rence 
Kiver.  .■').')ii  milesaway.t ')  In  Chicairo  the  <-ondit  ion- arc  somewhat  dif 
ferent.  and  practically  all  of  the  milk  used  there  i>  pioduccd  within 
loo  mdcs. 

"Siipcriof  li^'urcs  icI'.t  to  ilic  l.ilili.ii:rai>liv  at  tin-  .-iici  .>l   the  hull. •tin. 


6  BITREAU    OF    ANIMAL    INDHSTRY. 

Long  shipments  Imvo  necessai-ily  lentrtlioiicd  ven^  niatorially  the 
time  which  elapses  between  the  production  of  the  milk  and  its  con- 
sumption. A  considerable  part  of  the  milk  is  held  ten  or  twelve  horn's 
on  the  farm  before  it  is  delivered  at  the  milk  station,  and  another 
dela}'  frequently  occurs  at  the  city  depot  before  the  milk  is  distributed. 
Much  milk  reaches  Boston  from  18  to  30  hours  old.  (*)  The  greater  part 
of  the  New  York  milk  is  from  12  to  36  hours  old  when  it  reaches  the 
city.  Great  care  is  now  used  to  hold  the  milk  as  nearly  as  possible  in 
its  original  condition.  On  the  long  hauls  the  milk  is  cooled  at  the 
receiving  station  and  ice  is  used  to  hold  down  the  temperature  in 
transit. 

Notwithstanding  all  the  precautions  observed,  the  milk,  as  it  is 
delivered  to  the  consumer  in  the  city,  is  usuall}^  in  a  state  far  from 
satisfactor3^  On  the  average  farm  the  conditions  are  such  that  the 
milk  becomes  heavily  contaminated  with  various  kinds  of  bacteria.  If 
the  milk  is  not  cooled  at  once,  multiplication  of  these  soon  ])egins  and 
continues  with  more  or  less  rapidity,  which  depends  largely  on  the 
temperature.  Even  in  milk  held  at  comparatively  low  temperatures 
the  increase  ma}'  be  gi'eat. 

A  few  examples  of  the  bacterial  content  of  city  milk  will  serve  to 
illustrate  the  extent  of  this  contamination.  Sedgwick  and  Hatchel- 
der  f)  found  in  57  samples  of  Boston  market  milk  fi'om  30.000  to 
4,220,000  l)acteria  per  cubic  centimeter.  Hill  and  Slack  (*)  tubulated 
the  results  of  the  examination  of  2,39-1:  samples,  nearly  all  taken  as  the 
milk  arrived  in  the  city,  as  follows: 

Per  I'eiit. 

Below  100,000  Vjactt'ria  per  cubic  centimeter 42 

Between  100,000  and  500,000  per  cubic  centimeter 29.  75 

Between  500,000  and  1,000,000  per  cubic  (-entimeter J).  75 

Between  1,000,000  and  5,000,000  per  cubic  centimeter 12.  75 

Above  5,000,000  per  cubic  centimeter 5 

Uncountable  spreaders 0.  75 

Park  (■^)  gives  the  average  of  20  samples  taken  from  cans  inunediately 
on  arrival  in  New  York  in  March  as  over  5,000.000  per  cubic  centi- 
meter. The  average  of  13  samples  delivered  to  tenement  houses  in 
midwinter  was  1,977,692  per  cubic  centimeter,  while  early  in  Septem- 
ber it  was  15,163,()00  per  cubic  centimeter.  In  the  better  districts  at 
the  same  time  the  number  was  considerably  less,  Bergey  (")  found  the 
average  of  10  samples  collected  at  railroad  stations  in  Philadelphia  in 
July  to  be  4,802,355  ])er  cul)ic  centimeter.  It  is  i-eadily  s(»en  fiom 
these  figures  that  the  bacterial  cojitaminatiou  of  the  city  milk  supply, 
especially  of  the  larger  cities,  is  uniforndy  great. 

It  is  well  established  that  sjx'ci  tic  diseases  are  not  infrecpUMitly  spread 
through  the  milk  sup})ly.  Asid(^  from  this  im{>ortiint  phase  of  the 
question,  which  can  not  be  discussed  here,  it  is  well  known  that  bac- 
teria are  able  to  ))ring  about  in  niilU  many  changes  of  a  highly  unde- 
sirable nature.     These  vary  from  decompositions  scarcely  ati'ecting  the 


BACTERIA    OF    PASTEURIZED    AND    UNPASTEURIZED    MILK.  7 

taste  to  the  formation  of  products  of  a  vorv  toxic  nature;  the  most 
familiar  change  is  the  sourinj^.  or  curdlint;'.  resulting  from  the  acid 
fermentation  of  the  sugar.  While  this  spoils  the  milk  for  drinking 
purposes,  the  group  of  bacteria  which  brings  about  this  change  is  not 
considered  deleterious.  Indeed,  they  are  introduced  in  the  form  of 
artificially  prepaivd  cultures  in  the  manufacture  of  butter  and  many 
kinds  of  cheese.  On  the  othei*  hand,  there  is  normall}'  present  in  milk 
a  group  of  l)acteria  which  acts  on  the  nitrogenous  constituents — the 
casein  and  albumen-  and  their  decomposition  products.  These  bac- 
teria secrete  enzymes,  or  digestive  agents,  which  act  entirely  inde- 
pendently of  the  cell,  and  are  capable  of  bringing  about  digestive  action 
greatly  in  excess  of  the  needs  of  the  organism.  The  rennet  usually 
secreted  with  the  proteolytic,  or  digestive,  enzymes  curdles  the  milk, 
which  is  slowly  digested  until  in  time  the  curd  may  be  entirely 
replaced  by  a  clear  serum.  In  some  cases  the  digestion  nuu'  go  on 
without  previous  curdling.  As  milk  is  ordinarily  used,  this  process  is 
not  sufKciently  advanced  to  affect  the  appearance  or  taste  appiecia- 
bly,  although  it  would  probably  he  unusual  to  Hnd  milk  twenty-four 
hours  old  in  which  some  change  of  this  nature  had  not  taktMi  place. 
The  products  of  this  decomposition  may  be  entiridy  harmless  even 
when  taken  in  considerable  (juantities,  or.  on  the  other  hand,  they 
may  have  a  very  toxir  action. 

The  cases  of  ])tomaine  poisoning  fi'om  milk  occasionally  reported 
are  in  all  probal)ility  dnv  to  bacteria  of  this  class.  Such  cases  are  so 
inlre.iuent  and  usuallv  of  such  obscure  oritrin  ti)at  thev  need  not  t>e 
considered  in  a  discussion  of  the  genei-al  milk  supply.  Ilowcn'cr.  it  is 
generally  recognized  thai  children,  and  especially  children  under  one 
year  old.  may  ))(»  vei\v  sei'iously  all'ected  by  milU  containing  many 
bacteria  of  this  type.  The  I'elation  between  the  condition  of  tiie  milk 
and  the  amount  of  intestinal  trouble  in  young  children  has  been 
denionsti'ated  by  the  investigations  of  Park  and  Holt  <)  in  New  Voik 
("ity.  They  found  that  this  relation  held  for  very  young  childi'cn 
only,  and  did  not  hold  for  children  ovei'  thi'ee  years  old.  even  when 
they  were  fed  milk  containing  large  numbers  of  l):icteria.  They  were 
unable  to  find  any  relation  between  specilic  \arietiesof  bacttM'ia  occur- 
ring in  tlie  milk  and  the  health  of  childi'cn.  l-'oi'ty  per  cent  of  the 
cultui'es  tested  cau>-ed  death  when  injecte(l  int raperitoneally.  but  otdy 
one  of  bit*  caused  illness  or  death  when  (vd  to  young  kittens. 

It  is  prol)able  that  the  intestinal  troubhvs  of  childi'en  ai-e  not  all 
caused  l»\(»ne  or  t  wo  specilic  varieties  of  l)acteria.  Imt  that  they  may  be 
caused  by  any  one  of  a  numbei'  of  widely  (list  ributetl  specie--,  which 
may  under  certain  circumstances  prtxluce  al»nornial  conditions  in  the 
digesti\(>  tract.  This  may  be  brou<_'ht  about  either  through  the  direct 
action  of  the  bacteria  in  the  intestines  or  indirectly  l)y  the  forniati(.ii 
of  toxins  in  tlu'  milk  itself. 


8  BUREAU    OF    ANIMAL    INDUSTRY. 

The  great  bacterial  containiiiation  of  milk  is  now  well  recognized, 
and  the  public  interest  in  this  question  is  shown  in  the  municipal  con- 
trol which  is  now  very  generally  exercised  over  the  milk  supply.  The 
control  usually  takes  the  form  of  inspection  for  adulteration  and  the 
presence  of  antiseptics,  licensing  of  dealers,  and  in  some  cases  the 
inspection  of  the  dairy  farms,  with  certain  requirements  regarding 
their  sanitarv' condition.  In  a  very  few  cities  it  is  required  that  the 
milk  shall  not  be  above  a  certain  temperature  when  delivered,  and  that 
the  bacteria  shall  not  be  above  a  certain  limit.  The  city  regulations  of 
Boston  require  that  milk  shall  not  contain  over  500,000  bacteria  per 
cubic  centimeter. 

Another  method  which  has  been  adopted  with  good  results  in  some 
cities  is  the  inspection  of  the  dairies  and  milk  by  some  organization, 
usually  a  medical  society.  Dairies  meeting  the  requirements  of  the 
society  are  given  a  certificate  and  are  allowed  to  advertise  their  milk 
as  certified  by  the  society.  The  so-called  model,  or  sanitary,  dairies 
furnishing  milk  under  exceptionally  clean  conditions  are  becoming 
somewhat  numerous,  but,  as  they  are  obliged  to  sell  their  product  at 
an  advance  over  the  usual  price,  they  have  not  yet  become  an  impor- 
tant factor  in  the  general  milk  supply.  All  of  these  methods  are 
designed  to  prevent  the  contamination  of  milk  by  bacteria  or  to  inhil)it 
their  growth  while  the  milk  is  being  transported  from  the  farm  to  the 
consumer.  Although  they  have  doubtless  resulted  in  a  distinct  im- 
provement, it  is  evident  that  they  have  by  no  means  produced  a  perfect 
milk  supply.  An  ideal  milk  would  be  collected  under  perfect  sanitary 
conditions  from  healthy  cows  and  held  during  transportation  at  such  a 
temperature  that  the  few  bacteria  which  are  found  in  it,  even  under 
the  best  conditions,  would  have  no  opportunit}'  to  develop.  A  milk 
supply  of  this  nature  will  come  only  through  a  long  slow  process  of 
education  and  regulation.  In  the  meantime  milk  dealers  have  resorted 
to  various  methods  to  inhibit  or  destro\'  the  bacteria  already  present 
in  the  milk.  The  objection  to  the  use  of  antiseptics  is  so  strong,  in 
this  countr}'  at  least,  that  this  method  need  not  be  considered. 

PASTEURIZATION. 

A  method  which  was  at  one  time  looked  upon  as  in  some  respects  a 
solution  of  the  question  of  the  city  milk  supj)ly  is  the  ai)pli(ation  of 
heat  to  milk  in  such  a  mannei'  that  the  greater  part  of  the  bacteria  is 
destro3'ed  without  seriously  affecting  the  character  of  the  milk.  This 
process  is  known  as  pasteurization,  from  the  fact  that  it  was  tirst  used 
on  an  extensive  scale  in  the  wine  industry  of  Fiance  on  the  reconnnen- 
dation  of  Pasteur.  In  the  application  of  this  term  to  milk  it  is  fre- 
({uently  confused  with  sterilization,  which  involves  the  complete 
destruction,  not  necessarily  by  heat,  of  all  the  ))acteiia  present.  As 
commonly   practiced,    howevei",    pasteurization    did    not  produce   the 


BACTERIA    OF    PASTEURIZED    AND    UNPASTEURIZED    MILK.  9 

results  expected  and  its  use  jrmdually  declined.  Nevertheless,  the 
statistics  of  200  cities  and  towns  collected  l)y  the  Dairy  Division  (*)  show 
that  considerable  milk  is  still  pasteurized,  and  the  practice  is  probably 
gaining  somewhat  in  favoj*.  Of  the  1<)8  cities  answering  an  inquiry 
regai'ding  the  amount  of  milk  pasteurized.  S2,  or  about  50  per  cent, 
stated  that  more  or  less  milk  was  past<'urized.  I'sually  a  small  amount 
only  was  treated,  but  in  some  cities  it  was  given  as  from  10  to  50  per 
cent  of  the  total  supply.  Various  methods  of  pasteui'ization  are 
employed,  nearly  all  of  them  being  etlicient  if  propci'ly  used. 

To  be  efficient,  pasteurization  should  destroy  practical Iv  all  of  the 
bacteria  in  the  vegetative  stage.  This  may  be  accomplished  by  the 
application  of  a  comparatively  high  degree  of  heat  for  a  sliort  time  or 
of  a  lower  temperature  for  a  longer  period.  In  addition  to  being  effi- 
cient, the  method  should  not  give  the  milk  a  decided  cooked  taste.  In 
all  prol)ability  this  fault  has  been  responsible  for  the  decreased  use  of 
pasteurization.  MilkuKMi  have  been  careful  to  adopt  a  temperature 
low  enough  to  avoid  a  cooked  taste,  and  as  a  result  a  small  part  only 
of  the  bactei-ia  has  been  destroyed,  and  tiu>  increased  keeping  (juidity 
of  the  milk  has  not  been  sufficient  to  repay  the  extra  labor.  Further- 
more, a  method  to  ))e  practical  umst  be  economical  of  heat,  lal)oi-.  and 
time.  A  method  a})plicable  to  a  few  gallons  of  milk  can  not  be 
economically  apj)lied  to  sex'eral  hundred  or  a  thousand  gallons.  The 
simplest  a})paratus  for  pasteurizing  milk  is  a  vat  surroundc^d  by  a 
water  jacket,  with  some  aiM'angement  for  heating  the  watei".  In  the 
machines  of  this  tyi)e  the  milk  is  heated  to  the  desired  temperature 
and  held  for  some  tim(\  usually  15  to  ;>(•  minut(>s.  The  tem])erature 
re(iuir(Hi  for  etlicient  ])iisteuiMzation  is  d(^])endent  on  the  length  of 
ex})()sure.  'I'iie  thermal  death  point  of  tiie  tubercle  bacillus,  which  is 
the  most  resistant  of  the  known  nonspori'-forming  pathogenic 
bactiM'ia.  is  usually  taken  as  the  critei-ion  for  the  })roper  pasteurizing 
temperature. 

Recent  work  by  Tlieobahl  Smith  (")  and  Russell  and  Hastings  ('")  has 
shown  that  this  t)acilhis  may  Ix'  destroyed  l)y  an  exposure  foi'  15  to  •_'<• 
miiuites  ton  tenipei-atuie  of  ti(»  ('.  ( 1 4*  >  F.  I.  j)ro\  ided  that  the  milk  is 
thoi'oughly  stirred  to  prevent  the  foi'mation  of  a  liim  on  the  siiiface. 
In  practice  a  sliglitly  higher  temperatuiT  lis  71  (".(155  -Itio  F.) 
is  usually  adopted.  This  has  lieen  found  t<»  t)c  the  highest  temjxM-ature 
that  can  be  used  without  causing  a  distinct  cooked  taste. 

Another  appai'atus  which  has  been  generally  a(lo))ted  wlici-c  milk  is 
pasteurizecl  on  a  large  scale  iiivoh  c-.  the  continuous  flow  of  the  milk. 
In  this  case  the  milk  llows  o\er  a  hcatc(l  surt'aic.  w  here  it  is  laiscd  to 
the  recjuirecl  tempei'atui"«',  and  i)as-<(>->  on  in  a  lontinuous  .-"trcain  oxer 
the  cooler.  In  one  machine  of  tlii>  type  the  milk  |)asses  into  a  cylin- 
der, whcr(>  it  is  thrown  by  rapidly  rexolxing  j)a(ldle>-  in  a  thin  sheet 
on  the  iiuier  surface  of  a  >teani  jacket.  The  milk  i^  heated  ahiu»t 
:2i»ti();;  -No.  7;>— o.") l' 


10  BUREAU    OF    ANIMAL    INDUSTRY. 

instantly  to  any  tonipcniturc  desired  and  passes  into  tlie  cooler  after  a 
very  short  exposure.  In  an  improved  form  of  this  macliine  the  out- 
goings hot  milk  is  partially  cooled  by  flowing  back  over  the  incoming 
cold  milk.  One  pasteurizer  of  this  tjpe  is  so  arranged  that  the  milk 
flows  between  revolving  cylinders  containing  hot  water.  In  another 
type  the  milk  flows  slowly  through  a  vat  holding  revolving  disks 
filled  with  water  which  is  heated  by  a  jet  of  steam. 

On  account  of  the  short  exposure  the  temperature  necessary  to 
insure  efl5.cient  pasteurization  is  considerably  higher  than  that  used  in 
the  machines  giving  a  longer  exposure.  Harding  and  Rogers,  (") 
working  with  a  machine  of  the  continuous  rapid-heating  type,  found 
that  it  was  very  eflicient  at  80"-^  or  85^  C,  but  ineflScient  at  70'^  C. 
The  higher  temperatures  (80^-85 -'C.)  are  recommended  by  Bang,  (''^) 
because  the  tubercle  bacillus  is  certainly  destro3'ed  at  these  tempera- 
tures, even  with  the  very  short  exposure  secured  with  these  machines, 
and  the  milk,  in  addition  to  having  an  improved  keeping  quality,  may 
be  guaranteed  to  be  free  from  pathogenic  bacteria.  More  recent  work 
M'  Rusvsell  and  Hastings  Q^)  indicates  that  a  temperature  considerably 
below  80^-85^  C.  will  insure  the  destruction  of  the  tubercle  bacillus, 
even  with  the  short  exposure  obtained  in  continuous  pasteurization. 

Numerous  objections,  aside  from  the  extra  expense  and  labor,  have 
prevented  the  general  adoption  of  this  practice.  One  of  the  most 
valid  is  that  pasteurization  ma}'  be  used  to  correct  the  faults  of  Insani- 
tary conditions  and  thus  retard  the  progress  of  hygienic  methods. 
Milk  collected  under  cleanly  conditions  and  properly  transported  and 
delivered  does  not  need  pasteurization.  Another  serious  objection  in 
the  eyes  of  the  dealer  is  the  changed  condition  of  the  fat  globules. 
The  cream  separates  out  more  slowh',  giving  the  buyer  the  impression 
that  the  milk  is  deficient  in  fat.  The  taste  of  the  milk  is  also  changed 
more  or  less,  especially  if  the  continuous  machines  with  the  higher 
temperatures  are  used. 

The  question  of  the  comparative  digestibilitj' of  raw  and  cooked  milk 
has  been  much  discussed  and  investigated,  but  van  not  be  considered 
as  definitely  decided.  It  is  very  generalh'  believed  that  milk  which  is 
highh'  heated  is  somewhat  less  digestible  than  raw  milk,  and  ma\'  in 
some  cases  cause  pathological  conditions  due  to  improper  nutrition. 
On  the  other  hand,  it  his  been  shown  in  numerous  instances  that  chil- 
dren thrive  on  pasteurized  milk.  The  observations  of  Variot  ('*)  made 
on  3,000  infants  among  the  poorer  classes  of  Paris  fed  on  milk  steril- 
ized at  108^  0.  throw  some  light  on  this  important  question.  Three 
or  4  per  cent  of  these  children  could  not  use  this  milk,  })ut  the  remain- 
der, including  those  that  had  been  retarded  in  their  development  by 
gastro-intestinal  troubles,  did  well  under  this  treatment.  No  scurvy 
or  rachitis  was  observed  in  these  children. 

The   statement  has  frequently  been  made,  and   is  now  generally 


BACTERIA    OF    PASTP:URIZED    AND    rNPASTETTRIZED    MILK.        11 

accepted,  that  the  bacteria  developing  in  pasteurized  milk  arc  luiich 
more  undesirable  than  those  growing;-  in  raw  milk,  and  that  foi-  this 
n^ason  pasteurized  milk  may  become  actually  danti^erous  as  a  food, 
while  the  taste  and  appearance  remain  unchanj^ed.  It  is  a  matter  of 
common  observation  that  pasteurized  milk  fnMjuentl}'  decomposes  with 
a  rank  odor  without  soui"in*i;.  while  unlieated  milk  simply  turns  sour, 
curdles,  and  remains  imchanj^cd  for  some  time.  The  reason  for  this 
is  very  <'vident.  In  the  unheated  milk  the  lactic  bacteria  dexclop  enoi"- 
mously,  form inji"  acid  so  rapidly  that  the  «^n)wth  of  the  ))eptonizin<jf 
bacteria  is  checked  or  completely  pre\ cnted.  In  the  })asteurized  milk, 
on  (he  other  hand,  the  lactic  bacteria  are  usually  all  (lesti'oye(l,  leaviii<:f 
a  cl<>ar  tield  for  the  de\<'lopmeut  of  (he  moi'c  resistant  s])ore-formin»,'' 
peptonizin*;'  bacteiia. 

Conn  and  Ksten  ('')  state  that  the  de\  elopment  of  lactic  bacteria  serves 
as  a  protection  both  to  the  milk  and  the  jxMson  drinking-  it,  since  it 
prevents  the  o'rowth  of  other  bacteria.  Fluji*4e.("')  on  whose  work  most 
of  the  objection  to  pa.steurized  milk  is  based,  heated  milk  for  a  short 
time  at  1>0  -95C.  and  isolated  the  surviving- bacteria,  which  he  studied 
in  puiv  culture.  These  he  found  to  be  mostly  of  the  peptonizin*:;  and 
the  anaerobic  butyi'ic  acid  forms.  Some  of  the  formei'  pi'oduced 
danjjferous  toxins. 

WeberC')  found  that  most  of  the  bacteria  de\'elopinu-  in  so-caiiecl 
sterilized  milk  wei'ccf  the  hay  or  potato  l)acillus  type.  Fliiuoc's  toxin- 
forniinu-  bjicteria  wei'e  found  thice  times  in  the  15o  flasks  (wamined. 

It  is  easy  to  see  how  the  jjresence  of  considiM'able  numbers  of  bac- 
teria of  this  class  in  milk  \\h\  to  infants  mioht  cause  seiious  results 
either  thi'ou<ih  the  production  of  theii'  toxins  in  th(^  milk  oi-  aftei'  iKMnti- 
carried  themselves  to  the  (li<;('sti\'e  tract.  That  this  do(\s  not  alwavs 
hold  true  for  pasteui'ized  milk  is  well  illustrated  l)y  some  recent  woik 
by  Pai-k  and  Ilolt(')  in  New  ^'oi-k  City.  In  this  woik  the  conditions 
were  controlled  as  well  as  it  was  possible  in  in\('stiiiationsof  t  hi>  nature. 
About  .')0  babi«'s  wei'c  sel(>c(ed  from  the  tenement  houses  and  (li\  idcd 
as  accui'ately  as  j)ossibl(>  into  two  e(|ual  lots.  All  were  fed  on  milk 
moditi(>(l  at  one  of  the  Straus  milk  depots  and  were  treated  in  the  >ame 
way.  except  that  one  half  wei-(>  \'v^\  on  milk  ])asteurize(|  at  K'l.'.  V.  for 
thirty  miiuites  and  the  other  half  recei\  ed  the  same  milk  without  heat 
ini^f.  The  raw  milk  axcrajicd  in  the  mornino-  l.ijoo.ddo  bacteiia  per 
cubic  centimeter  and  the  pasteuiized  about  l.oiio  |)cr  cubic  cent  inictcr. 
while  in  the  aftcMMioon  of  the  same  day  they  contained  respect  i\ely  about 
•_'(),()(  10, 000  and  ao.ooo  l>acteria  per  cuttic  centimeter.  In  <li>cussinj:- 
the  residts  of  their  inxcst  illations  the  authors  say: 

Witliiii  one  week  "JO  nf  the  27  infants  |>ut  imi  tin-  raw  milk  siil'lcicii  from  moiicratc 
or  severe  diarrlu'a,  wliile  <lnriiiy  tlie  same  time  only  •">  cases  of  mi"ierate  ami  none  «>f 
severt'  (liarrln-a  ocenrreil  in  tliose  taking  pastenrizeii  milk.  Within  a  month  >^  of  tlie 
27  had  to  be  changed  from  raw  hack  to  heate<l  milk,  iM'canse  i>\   their  continucl 


12  BUREAU    OF    ANIMAL    INDUSTRY. 

illness;  7,  or  25  per  cent,  did  well  all  summer  on  raw  milk.  On  the  other  hand,  of 
those  receiving  the  pasteurized  milk,  75  per  cent  remained  well,  or  nearly  so,  all 
summer,  while  25  per  cent  had  one  or  more  attacks  of  severe  diarrhea.  There  were 
no  deaths  in  either  group  of  cases. 

Very  similar  results  were  obtained  from  a  second  trial  made  in  the 
same  manner  during  the  following  summer.  Doctors  Park  and  Holt 
were,  however,  unable  to  find  that  pasteurization  of  the  milk  affected 
the  amount  of  intestinal  trouble  in  older  children. 

These  results  may  be  taken  as  conclusive  evidence  that,  under  cei- 
tain  circumstances  at  least,  poor  city  milk  is  rendered  a  8afer  infant 
food  by  pasteurization.  It  must  be  remembered,  however,  that  this 
work  was  done  under  carefully  controlled  conditions  and  that  the  milk 
was  given  out  in  small  bottles  only,  so  that  it  had  to  be  used  before 
there  was  time  for  any  great  development  of  deleterious  bacteria. 

Park  and  Holt,  in  the  paper  cited  above,  express  the  belief  that 
intestinal  troubles  in  children  fed  on  poor  milk  which  had  been  pas- 
teurized were  due  to  changes  in  the  milk  which  were  not  neutralized 
by  heat.  Lii))bert,  ('*)  on  the  other  hand,  stsites  that  the  toxic  prop- 
erties of  a  milk  culture  of  one  of  Fliigge's  peptonizing  bacteria  were 
destro^^ed  by  heating.  The  results  touching  on  this  question  are  not 
conclusive,  but  it  seems  probable,  when  the  comparatively  stal)le 
nature  of  the  known  toxins  is  considered,  that  the  toxicity  of  badly 
infected  milk  would  not  be  decreased  by  the  heat  received  in  ordinary 
pasteurization. 

We  have  seen  by  this  brief  review  of  the  literature  on  milk  supply 
that,  notwithstanding  the  increasing  stringenc}-  of  municipal  regula- 
tions and  efficiency  in  their  enforcement,  the  milk  is  usually  badly 
contaminated,  frequently  even  to  the  point  of  becoming  positively 
dangerous  when  used  as  a  food  for  infants;  that  some  authorities 
consider  pasteurization  an  advisable  remedy  for  this  condition,  and 
that  this  method  is  used  in  man}-  American  cities.  On  the  other  hand, 
it  appears  that  some  people  consider  that  the  bacteria  which  develop 
in  milk  after  pasteurization  make  it  more  dangerous  than  poor  raw 
milk. 

EXPERIMENTS   WITH    RAW   AND    PASTEURIZED    IVULK. 

It  is  undoubtedly  true  that  bacteria  of  a  very  undesirable  nature 
ma3'  develop  in  the  clear  field  left  by  the  destruction  of  the  lactic 
bacteria,  but  how  soon  they  develop  after  pasteurization,  what  num- 
bers they  must  attain  befoi'e  the  milk  becomes  dangerous,  and  how 
their  development  compares  with  the  growth  of  similar  bacteria  in 
unheated  milk,  are  questions  which  have  not  yet  been  answered.  The 
writer  has  been  unable  to  find  the  results  of  any  investigations  giving 
the  quantitative  bacteriological  examination  of  pasteurized  milk 
beyond   the   number   present   immediate!}'   after   pasteurization.     In 


BACTEKIA    OF    I'ASTKUKIZKD    AND    UNPASTEURIZED    MILK. 


13 


undertaking  the  work,  the  results  of  which  are  t>;iven  in  this  pa])er,  it 
was  not  intended  to  attein|)t  to  denionstrate  that  it  is  advisable  to  pas- 
teurize or  that  it  is  inadvisahle.  hut  to  determine  tiie  rapidity  of  bac- 
terial develo])nient  in  heated  milk  and  to  compare  it,  (|uantita(ively  and 
(lualitatively,  with  the  flora  of  raw  inilk.  It  was  plamied  at  the  l»egin- 
ning  to  make  this  investij^ation  more  comprehensive,  but  ceitain  cir- 
cumstances have  interfe!"ed  to  present  its  completion  at  this  time.  It 
is  l)elieved,  however,  that  the  results  ali'c^ady  obtained  ai'c  of  sullicient 
value  to  warrant  their  pul)lication  in  this  incomplete  condition. 

The  milk  used  in  this  work  was  all  obtained  from  a  larj[r(>  dairy  with 
an  excelU'nt  reputation.  When  delivered,  the  milk,  which  was  the 
mixed  milk  of  several  herds,  was  24  to  3<)  hours  old.  The  tirst  nine 
samples  were  held  overnig'ht  in  a  refrigerator  to  allow  bacterial 
devel()[)ment  corresponding  to  that  of  the  oldest  city  milk.  The 
remaining  samples  wei'c  pasteurized  when  received  that  is,  when 
24  to  8<)  hours  old.  Although  no  compndiensive  bactcM'iological 
examinations  of  the  milk  su])ply  of  Washington.  I).  ('.,  have  been 
published,  the  results  of  the  following  determinations,  made  (with  (he 
exception  of  Nos.  1  and  '2)  in  March  and  A})ril.  indicate  that  thesr  may 
be  taken  as  fairly  i"(>presentative  of  the  milk  deiivei-ed  by  the  large 
\N'ashini»'ton  daii'ies  durini>'  the  warm  months: 


Taui.K    I.  —  I'xicti  r'ln  in  milk  from  niri(>i(t< 


ill   ]Vas},iii<ihm.    I>.    C. 


()l>lHiiu'(l  inm 


1     Sjitiitiiry  dairy 

■J    (1(.  

:!  I'riviitc  city  iliiiry 

I     (inx'fry  slorc 

r>     City  ilairy  

ti    do  


Lactic  iicid. 


Pit  CI  lit. 


U.  Ill 

.  I  jr. 


Total  l)a. 
Icria. 


l(i,s,  (HKI 

lis.  .Vmi 

l;i,  I'^Kt 

;>.  77.'..  (KNt 

ii;.s.")0,  iKKi 

s'l,  (KM 


Ccptoiiiz- 

iiiK  liac- 

tcria. 


IIP-J.(HH1 

0 
1:>7.-'>(KI 


In  carrying  out  the  work  outlined  in  the  introduction  it  is  essential 
tirst  of  all  that  the  pasteurization  be  eflicient.  Thi>  method  by  which 
this  result  is  obtained  is  not  important.  For  the  sak(>  of  com cnience 
asmall  model  made  for  this  work  was  used,  with  a  tempeiat lire  of  s.', 
('.(IS.-)  F.).  This  ai)parat  us  consisted  of  a  small  trough,  with  an  inlet 
and  an  out  let  t  ul»e  at  opposite  ends;  a  sei'ies  of  revolving  hollow  disks, 
soiirranged  that  steam  could  be  blown  t  hi'ough  them,  served  the  double 
purpose  of  heating  and  stirring  the  milk.  The  milk  tlowe(|  in  at  one 
end.  was  heated  to  the  i'e(|uii-(Ml  temperature,  and  i)as>ed  out  and  oxer 
th<^  sui'face  of  a  cooler  which  brought  the  temperature  down  to  about 
'i<>--J.")  ('.  The  temp(M"atiire  adoi)ted  (1S,'>  V .)  is  higjier  than  is  oidi- 
narilv  used,  and    milk  treated   in  this  wav  has  a  distinct  cooked  taste; 


14  BUREAU    OF    ANIMAL    INDU8TRY. 

but,  since  this  work  was  arranged  onlj'  to  study  the  bacteria  g^rowinj^ 
in  efficii'ntly  pasteurized  milk,  this  fact  was  of  no  importance  in  this 
instance.  Three  samples  were  collected  in  sterile  flitsks — one  from  the 
milk  before  pasteurization  and  two  of  the  pasteurized  milk.  One  of 
the  latter  was  placed  in  a  refrij^erator  kept  uniforndy  at  10'^  C.  (50°  F,), 
and  the  oth«M"  was  kept  (with  the  exception  of  a  few  samples  which 
were  held  in  the  laboratory)  in  an  incubator  holding  uniformly  at  20'-' 
C.  (68°  F.).  In  like  manner  half  the  samples  of  raw  milk  were  held  at 
20°  C.  and  the  other  half  at  10°  C.  Gelatin  plates  were;  made  from 
each  sample  at  the  time  of  pasteurization,  and  at  intervals  of  6,  12, 
and  24  hours,  up  to  96  hours,  or  until  the  milk  curdled.  Two  and  one- 
half  per  cent  lactose  gelatin  was  used.  A  series  of  dilutions  in  sterile 
water  was  made  so  as  to  get  as  nearly  as  possible  300  or  400  colonies 
on  a  plate.  When  the  lactic  bacteria  became  numerous  the  li({uefiers 
were  counted  on  plates  containing  several  thousand  colonies.  Although 
this  method  is  probably  inaccurate  it  enables  one  to  count  many  of  the 
less  numerous  species,  which  would  be  missed  in  a  dilution  suited  to 
the  lactic  forms.  All  small  spherical  solid  colonies  were  counted  as 
lactic-acid  bacteria.  While  this  grouping  would  probably  include 
many  inert  forms  the  error  would  not  afi'ect  the  results  seriously.  The 
plates  were  incubated  at  20°^  C  until  the  spread  of  liquef3ing  colonies 
made  it  necessary  to  count.  In  many  cases  this  became  necessary 
before  some  of  the  slower-growing  colonies  had  ap[)eared.  No  attempt 
was  made  to  stud}"  the  various  species  beyond  what  was  necessary  to 
determine  the  relationship  of  the  colonies  occurring  on  the  different 
plates.  In  the  tables  the  bacteria  are  arranged  in  four  different 
groups — the  total  bacteria,  the  acid-forming  bacteria,  the  peptonizing, 
or  liquefying,  bacteria,  which  are  subdivided  into  the  slow  and  rapid 
liquefiers,  and  the  inert  bacteria,  or  those  having  no  appreciable  effect 
on  milk.  The  action  on  milk  was  determined  by  transferring  a  num- 
ber of  type  colonies  from  each  sample  to  litmus  milk  and  incubating 
for  several  da^s  at  30°  C. 

The  acidity  of  each  sample  of  milk  was  titrated  against  I'oNaOH 
with  phenolphthalein  as  an  indicator  when  the  gelatiti  plates  were 
made,  and  the  appearance  and  taste  of  the  milk  usually  noted  when  it 
curdled,  or  at  the  end  of  96  hours. 


BACTERIA    OF    PASTEURTZED    AND    UNPASTEURIZED    MILK.       15 


Sample 
No. 


U 
21 
31 

12 
22 
32 

13 
23 
33 

11 
21 
31 

15 
2f> 
3o 

16 

2i; 

m  \ 

17  j 
27  I 
37 

1« 
2.S 

:« 

19 

2y 

3'.» 

nil 

210 

:<io 
111 

211 
311 

112 
212 
312 

113 
213 
313 

111 
211 
311 


Taijlk  it. — Phyitlcal  conditvm  nndtttMt'  of  tin-  milk. 


'I'reiitiiKMit. 


Raw 

F'usteiirized . 
do 


Kaw 

I'listeurizi'd  , 
do 


Kaw 

Pasteurized  , 
do 


Kaw 

I'asteiirized  . 
do , 


Kaw  

Tasteurized  . 
do 


Kaw 

Pasteurized 
do 


Kaw 

Pasteurized 
do 


Kaw 

Pasteurized 
<li. 


Kaw  

Pasteurized  . 
do 


Kaw  

Pasli'urized 


K.iw 

Pasteunzc< 


itaw 

I'Mvifiirized 


Knu    

Piisteuri/i'd 
.1.. 


ature. 

°C. 
R(K)m. 
K<H)in. 
10 

10 

R<K)in. 

10 

Room. 

RfKlUl. 

10 

10 

Room. 

10 

Room. 

Room. 

10 

10 
20 
10 


I  fours. 

72 

72 
120 

9f. 
96 
96 

48 
24 
9t; 

96 
W) 
96 


Acid  curd. 

Curdled  with  slight  digestion  and  gas. 

Appearance  unchanged;  sweet  taste. 

.Veid  taste. 

Curdled;  peculiar  nutty  (xlor. 

Cnclianged;  slight  off  taste. 

Partly  curdled. 

Lost. 

Marked  odor  of  raw  oysters. 

Not  curdled;  plea.sant  acid  taste. 
(Mirdled;  hitter  taste. 
Slight  nutty  flavor. 

Curdled;  pleasant  aciil  taste. 
Slight  oiT  flavor. 
Sweet;  uuehangeil. 

Not  curdled;  acid  taste. 
Curdled;  plea.sant  acid  taste. 

Sweet. 

Curdled;  aciil  with  slight  cheesy  taste. 
Curdled;  pleasant  acid  taste. 


-u  ( 


Acid  taste. 
Rciiticl  curd. 
Sweet. 

Curdled;  gas. 
Keiiiut  curd. 
Sweet. 

Acid  curd. 

KeiHiel  rurd.  disagreeahle  taste. 

Swi'Ct. 


_'(> 

4.S 

Acid  eunl. 

20 

l.s 

Cur.lled., 

10 

".M'l 

Sweet. 

Pa.--leurized 


Not  curdled:  clieoy  inhir. 
('iir(lle(l;  hitter  a^lrini:i'iit  tasit 


(  urdliMl.  ileaii  iieid  tasit 
Keniii'l  eiinl 


~iinr  la-le;  nut  eunlled. 
(Iinlled.  sliglil  digestion. 


It  will  1k>  noticed  that  the  luihcatfd  milk  held  at  'Jo  (\  usutilly 
curdled  in  4S  to  T'J  hours  with  an  acid  taste.  althou<rh  at  tini(>s  there 
were  indications  of  pcptoni/.ation.  In  the  raw  milk  at  1"  C.  the 
curdliii','-  wiis  much  retarded  and  tho  taste  was  atlected  hy  prestMice  of 
diiivstine"  l»acteria  in  (tne  or  two  castas.  The  |)asteurized  milk  held  :it 
'20'^  C,  on  tlu>  other  hand,  usually  had  a   rennet  curd  at  the  end  of  IS 


16 


BUREAU  OF  ANIMAL  INDUSTRY. 


hours,  with  a  disagreeable  taste,  although  in  a  few  instances  the  lactic 
bacteria  were  evidently  not  entirely  destroyed  and  formed  an  acid 
curd  in  48  hours.  The  pasteurized  milk  held  at  10'  C  almost  without 
exception  remained  perfectly  sweet  to  the  taste  and  unchanged  in 
appearance  for  96  hours  or  more. 

Table  III. — A(ndity  of  milk  expressed  as  per  cent  of  lactic  acid. 


No. 


11 

21 
31 

12 
22 
32 

13 
23 
33 

H 
24 
34 

15 
2.5 
35 

16 
26 
36 

17 
27 
37 

18 
28 
38 

19 

29 
39 

110 
210 
310 

111 
211 
311 

112 
212 
312 

113 
213 
313 

114 
214 
314 


Treatment, 


Teniper- 
I    ature. 


'  °C. 

Raw {  Room. 

Pasteurized j  Room. 

do 10 


Raw '  10 

Pasteurized [    Room. 

do !  10 


Raw J     Room. 

Pa-steurized Room. 

do \  10 


Raw 10 

Pasteurized Room. 

do 10 


Raw I     Room. 

Pasteurized Room. 

do 10 


Raw 

Pa.steurized. 
do 


Raw 

Pasteurized. 
do 


Raw 

Pasteurized. 
do 


Raw 

Pasteurized. 
do 


Raw 

Pasteurized . 
do 


Raw 

Pasteurized. 
do 


Raw 

I'asteurized . 
do 


Raw 

Pasteurized . 
do 


Raw 

Pasteurized . 
do 


Percentage  of  lactic  acid  after  lapse  of- 


.162 

.162 

.162 

.126 

.162 

.126 

.126 

.144 

.126 

.126 

.126 

.126 

.216 

.144 

.144 

.144 

.144 

.144 

.126 

.180 

.  126 

.144  i 

.126 

.126 

.144 

.162 

.144 

144 

.144 

.  126 

20 

.108 

20 

.108 

10 

.108 

10 

.  126 

20 

.126 

10 

.  126 

.126 
.126 
.126 

.126 
.126 
126 


.162 
.  126 
.126 

.  126 
.  126 
.126 

.162 
.  126 
.126 

.  126 
.126 
.  126 


.480 
.108 
.126 

.162 
.108 
.126 

.414 
.144 
.144 

.  162 
.144 
.144 

.  2.")2 
.  126 
.144 

.  162 
.126 
.  126 

.  2.i2 

.  126 

126 

.144 
.  126 
.  126 

.306 
.  12t; 
.  126 

.144 
.  126 
.126 


24 
hours. 


Perct. 

0.234 

.110 

.126 

.324 
.144 
.144 

.342 


.144 

.162 
.126 
.126 

.270 
.144 
.144 

.144 
.126 
.108 

.694 
.144 
.144 

.180 
.144 
.126 

.486 
.  126 
.  126 

.162 
.126 
.  126 

.448 
.  126 
.  126 

.144 
.126 
.126 

.666 
.126 
.126 

.126 
.  126 
.126 


48  72      I      96 

hours,    hours.  ]  hours. 


Perct. 

0.594 
.126 
.126 

.432 
.144 
.144 

.648 


.560 
.126 

.468 
.180 
.162 


.144 

.230 
.•126  j 
.126 

.504 
.144  ! 
.144 

.  162 
.666 


.486 
.180 
.126 

.702 
.162 

.  126 

.216 


Perct.  \  Perct. 
0.720   


0.126 


.522 
.645 
.162 


.306 

.630 
.216 
.126 


.216 
.126 


.126 

.126 

.126 

.864  . 

.702  -- 

.144  1 

.144 

.234  i 

.342 

.612 

.162  . 

.126 

.  12t> 

.126 

.810  . 

.162  .- 

.126 

.126 

.144 

.  270 

.648 

.  666 

.144  . 

.141 

.126 

.126 

.".T»i 



.4t>H  

.126 

.  126 

.144 

.  162 

.306 

.  126  . 

.  126 

.  126 

.  126 

.141  

.  126 

.126 

.  126 

.144 

.  2.'>2 

.  324 

.144  . 

.126 

.126 

.126 

BAOTKRIA    OF    PASTEURIZKD    AND    UNPASTEURIZED    MILK.       17 

For  ooMV'Cnieiice   of   comparison    these   results   are   averaged   and 
arranged  in  Table  IV. 

Taijlk  I V. — Average  increase  in  aciditif  of  milk  exprensett  as  jier  cent  of  lactic  add. 


TreatiiH'iit. 


PercenUige  of  luetic  iici<l  after  lapse  «f — 

0      1        6        '       12  24  4«  72  % 

hours.  ;  liours.  j  hoiir^.     hours,     hours,     hours,     hours. 


Per  ct.  Per  el.  Ptr  it.  I'lr  rl.  I'rr  rt.     Prr  rl.     Ptr  ct. 

Raw  milk  kept  at  20°  C i    0.131  0.  IW  0.25^1  0.4-19       0.0%       0.711     

Pa.steurize(l  milk  kept  at  20°C 134  .134  .127  .130        .2;'.l 

Raw  milk  kept  at  10° C 13C  .152  .  1C.7  .177         .2:« 

Pasteurized  milk  kept  at  10°  C 134  .129  .131  .129        .129 


.271 

.  3,\S 

.  i;«) 


0.  :i59 
.497 
.132 


As  would  naturall}'  l)e  expected,  the  increase  in  acidity  of  the 
unheated  milk  was  much  more  rapid  at  20  C.  than  at  lo  ('.  The 
average  of  the  increase  in  acidity  of  the  pasteurized  milk  at  2(»  C. 
does  not  express  the  true  state  of  atiairs,  as  the  increase  was  usually 
very  slight,  except  in  a  few  instances  when  the  rapid  multij)lication  of 
lactic  bacteria  caused  a  sudd(Mi  and  marked  increase  in  the  acidity. 
In  {\w  pasteurized  milk  at  10  ('.  thei'e  wtis  usually  no  increase  what- 
ever, iind  in  one  lot  only  was  there  sutlicient  acid  to  atl'ect  the  taste. 

The  com])lete  rt^sults  of  tlu^  bacteriological  counts  are  givtMi  in 
Table  \'.  These  are  summai'ized  in  Table  \'I,  which  contains  the 
mean  of  the  total  t)acteria,  and  in  Table  VIII.  which  contains  the 
mean  of  the  peptonizing  bticteria. 

Tahi.e  \ .  —  llacterid  per  cuhir  niitimetir  i  if  milk,  arnnigcd  in  (jrotipK. 
Samfi.k  No.  11.— Raw  Mii.k   Kf.it  at  Kuom  'ri..Mi'Ki!ATiKK. 
Numl)er  of  hiu'tena  found  after  lapse  of— 


CJroup. 

0  hours." 
h3.i,  000 

6  liours. 
12,cS2.'),000 

12  hours. 

21  hours. 

t)7i,r>(K).  uoo 

IS  luairs.       72  1 
.'WiO.  (ij:.,  (iot»  i.'xi. '. 

ours.       >,H 
:;7,ixKi ... 

1  hours. 

I'y,  032,  .^>00 

Total  li(iueliers. .. 
Rapid  li(|Ueliers  . . 

(•),  .MX) 

2."),  tH)0 

■22.'i,  tKK) 

1.'.<3-',6<I0 

MKI.  (MN) 

0  . . . 

Inert 

Total  haeleria  . . 

Total  lactic 

Total  iKiueliers. 
Kapiil  lii|Uclicrs 
Slow  li(|ueliers  . 
Inert 


SaMI'I.K   No.  21— I'ASTKIKIZKD    Mll.K     K  KfT    AT    KooM     I' IM  IKK  ATT  KK 
■IS  I'.lh  .'-•D 


IW 
4 


N) 


l.tKHI 


1.7IKI,  (RKI 


l.fJ.lKHl.OOO 
132.000,  (HKt 


Samim.k  No'.  :il.— I'astki  i'.i/.Ki>  Mii.k  Kki-t  at  Ut    (' 


Total  bacteria  . . . 

Total  lactic 

Total  lii|Ueliers.. 
Rapid  liiiueliers  . 
Slow  li(iuetiers  . 
Inert 


3I,S 
0 

7 


4..>70 
0 

:«o 

4..'vio 


2.11: 


I'.'T.IHKI  ivS,  s:{(l.  IKK) 

(I  II 

2,  JOO  '.fJO.  IM) 


(iThe  Mne  of  the  milk  K'lveii  in  the  tahles  is  reckoned  frmii  Ihe  lime  of  pasleiiri/aliou 
t  Dilution  too  low. 


18 


BUREAU    OF   ANIMAL   INDUSTRY. 


Table  V. — Bacteria  per  mbic  centvnder  of  mUk,  arranged  in  groups — Continued. 

Sample  No.  12.— Raw  Mii.k  Kkpt  at  10°  C. 


Group. 

Number  of  bacteria  found  after  lapse  of— 

0  hours. 

6  hours. 

12  hours. 

24  hours. 

48  hours. 
618,000,000 

72  hours. 

96  hours. 

Total  bacteria  — 
Total  lactic 

103,926,000 

139.500,000 

153,000,000 

266,000,000 

152,500,000 

354,000,00C 

Total  liqiierters... 

75,000 

100,000 

500,000 

:::;;::::::: 

Slow  liquefiers  ... 

Inert 



Sample  No.  22.— Pasteurized  Milk  Kept  at  Room  Tempebatcre. 


Total  bacteria 

Total  lactic 

70 


23 

50 

1,200 

1,475,000 

1,175,000 

7,500 

40,740,000 

40, 440, 000 

150,000 

308,000,000 
298, 750, 000 

Total  liquefiers... 

4 

0 

8 

800 

800 

0 



Inert 

225,000 

150,000 

9, 250, 000 

Sample  No.  32.— Pasteurized  Milk  Kept  at  10°  C. 


Total  bacteria 

Total  lactic 

70 

70 

30 

60 

70 

6 

60,600 
59,800 

Total  liquefiers... 

4 

4 

2 

10 

6 

300 

Inert 

500 

Sample  No.  13.— Raw  Milk  Kept  at  Room  Temperature. 


Total  bacteria 

Total  lactic 

Total  liquefiers  ... 
Rapid  liquefiers  .. 
Slow  liquefiers  ... 
Inert 


33,707,500   83,062,500168,812,500 

32,945,500  80,830,500165,625,000: 

762, 000     2, 232, 000     3, 187, 500 


231,750,000     947,260,000;. 
226,937,500     946,7.50,000. 

4, 812,  .500'  500,000. 

1,812,500! 

3,000,000 :. 


Sample  No.  23.— Pasteurized  Milk  Kept  at  Room  Temperature. 


4,040 

29,320 

(n)                 (6) 
1 

Total  lactic 

Total  liquefiers  . . . 

11 

50 

1 

Sample  No.  33.— Pasteurized  Milk  Kept  at  10°  C. 


Total  bacteria 

Total  lactic    

4,040 

6,390 

46, 150 

843,000 

Liquefied. 

34,375,000i  247,750,000 
l,875,000i      29,2.50,000 

Total  iiqueiiers... 

12 

190 

720 

4,500 

5, 000, 000  3, 000. 000 
2, 625, 000 

2, 375, 000         3. 000.  WH) 

27,500,000     215,500,000 



a  Dilution  too  low. 


b  tlask  broicen. 


BACTERIA    OF    PASTEURIZED    AND    UNPASTEURIZED    MILK.       19 

Table  V. — lincli'ria  /u'r  cufiic  ceiifinii'ttr  of  milk,  (trranyi'l  in  (jruK/tx — Continued. 
Sampi.k  No.  14.— Kaw  .Mh.k   Keit  at  lO'M'. 


Group, 


Nuiiilicrof  InicU'ria  foiiinl  iifttT  liipse  of — 
0  liniirs.       tl  hoiiiN.       12  hours.       '24  hours.  4,s  hours.       72  hours,  i     9<i  liourK. 


Total  hlictpria 11,12;'>,0«0    HI,  I'A'i.OOO    ]"J,iV).000     ms, r)00, 000     ak),rHX),UOO(»H2,7.V>.  0001, 102,000,000 

Toml  iuctic 


ToUil  liciUt'fuTs...  I40,(KK)         loV.OOO     ;{,:jr_',(HX)         5,250,000         y,:«7,.'>oo 

Kiii)id  liquefiers  . . I         .'»5. 000 7.=J>.  <KK) 

.Slow  liqueflers «5, 000 2,  .5(12. 000 


l«,000,Ouo        11,025,000 


SAMI'LE    No.  24.  — I'ASTKIKIZKD    MlI.K    KKIT    at    KooM    TE.MI'KKATIUK. 


Total  bacteria 

Total  lactic- 

50 

50 

30 

8,500 

4y,  (KJO,  000 

471, .500. 000  1,043,000,000 

Total  liiiuflii-rs  . . . 
Kapiil  li(iU('tiers  .. 

10 
10  .... 

(J 

10 
10 

2,  7.50 
2,  7M) 

X,  -.iCA).  (KK) 

1,.'>40,  (HHI 

t;.  h20.  (KK) 

41,240.(HIO 

w,  (MJo,  6()6     iii,t)66,6o6 

37.500,000 

52  'itK)  000 

Inert 

5,  7r)0 

iWl ,  .'KK),  000 

1 

1 

'AsiEim/K.ii  .Mii.K   Kkit  at  10"  C 


Total  bacteria  . . . 

Total  lactic 

Total  li(|Uctiers.. 
Rapiil  li<iucticrs  . 
.silow  li<)uclicrs. .. 


M.><,000   21,fi00,(K)0     277,250,000 


30.9(K)    11,200,IKX) 

U .  5(K) 

l'.».  100 , 


40,  7.50. 000 


Samci.k.  No.  15.^Ka\v   Mii.K   Kkit  at  K(mim    Ikmi-kka  ii  iti: 


Total  bacteria  . 

Total  l;ictic 

Total  li(|iielicrs 
Kapiil  lii|tielier 
Slow  li<|Uetiers 
Inert 


3,  12:!,  7:50  13.  725.tHH»  tKi,  025,  000  l.')h,  7.50,IKH) 

2,  Wl.  2.^)0  12.  100,  IKK)  (;,!,  175,  (HKl  l;!.s,  .'KKI,  (HKI 

132,  r)(H)  '.MKI,  IRH)  l.S(KI.(HKI  HI,  2r)().  (KH» 

70,  (KKI  l.'ill,  IKKI  7.'>(I,IKI0  5,  (KMI.  (XHI 

i;2.5(K)  1,50,  (KKI  I.O.'Ml.tKHI,  5.2-')0,  (KKI 

125,  (HKI  1,3.'>0.(HK)1  Id,  (KKI.  (KKI 


■>.I5.  000,  (KKI  I'^SO.  ,5(K),  000 

i73,  .'HKI.  (KKI  072.  025,  IHKI 

H.IHXI,  (KKI      4.12-5,  (KHl 

."HK),  (KKI      2,7."H>,  (KK) 

5..')(HI,  (KK)      l.:;75,(HKI, 

IS,.5(KI,(KHI      '.t,  7.'>0.  tMKI  . 


Total  bacteria  . . 

ToUil  lactic 

Total  li(|(ielicrs. 
Kai)iil  lii|Uc(iiTs 
.*-;io\v  li(iiiclicrs  . 
Iiieit 


—  I'Asi  KrKi/.i;i>  Mii.K  Kkit  .\r  Room  Tkmi'kkatikk. 

.50  .'HI  2(K)  l,(KKli     ;!.525.l 

0                        0  2(KI| 
2(Hl| 


I,  (HKI      3..525.(KK) 
I,  (KKI;     3.  .525.  (KKI 


-I'ASI  kiiiizku  Milk    Kkit  ai    Id     (' 


Total  bacteria  . . 

Total  lactic 

Total  lii|iielitTS  . 
Kiipid  liiiiielicrs  , 
Slow  liipiclicrs  . 
Inert  


11(1 
0 


1(1 

I'.,  KHI 


20 


BUREAU    OF   ANIMAL    INDUSTRY. 


Tablb  V. — Bacteria  per  cubic  centimeter  of  milk,  arranged  in  groups — Continued. 
Sample  No.  16.— Kaw  Milk  Kept  at  10°  C. 


Group. 

Number  of  bacteria  found  after  lapse  of—                             « 

0  hours. 

6  hours. 

12  hours. 

30,875,000 

29,200,000 

1,400,0(X) 

1,100,000 

300,000 

275,000 

24  hours. 

48  hours. 

72  hours. 

96hoiin. 

Total  Ikftflfcferia.... 

Total  lactic 

Total  llquefiers... 
Rapid  liquefiers . . 
Slow  liquefiers  . . . 

5,325,000 

4,  .550, 000 
125, 000 
75,000 
50,000 
650,000 

21,500,000 
18,000,000 
1,500,000 
600,000 
1,000,000 
2, 000, 000 

75,000,000 
70,5.50,000 
2,  .500, 000 
2, 500,  OoO 

314.000.000 
28!},  2.50, 000 
24,2.50,000 
21,2.50,000 
3,000,000 
6,500,000 

Plates 
liquefied. 

480, 5106,600 
878,000,000 
99,000,000 
65, 500, 000 

1,750,666 

:{  .5(X)  IMM) 

Sample  No.  26.— Pasteurized  Milk  Kept  at  20°  C. 


Total  bacteria .... 

20 

40 

220 

1,040,000 

960,000 

80,000 

10,000 

70,000 

1,681,000,000 
1,-581,000,000 

Total  lactic 

Total  liquefiers... 

0 

30 
10 
20 

96 
90 

Sample  No.  36.— Pasteurized  Milk  Kept  at  10°  C. 


Total  bacteria . . . 

Total  lactic 

Total  liquefiers.. 


20 


20 


•30 


110 
"'16 


2,430 
2, 430 

0 


67,900 

67,880 

20 


Sample  No.  17.— Raw  Milk  Kept  at  20°  C. 


Total  bacteria . . . 

Total  lactic 

Total  liquefiers.. 
Rapid  liquefiers. 
Slow  liquefiers... 
Inert 


37, 950, 000 

34,726,000 

3, 075, 000 

25,000 

3,0.50,000 

150,000 


136,000,000  317,000,000 
110,7.50,000  31-1,7.50,000 
24,600,000;     1,7.50,000 


1,250,000 

23, 250, 000 

750,000 


500,000 

1,250,000 

500,000 


78, 000, 000 


1,000,000 

"i,  666,066 


452,600,000, 

4.52,350,000 

2.5,000, 


26, 000! 
125,  OOOi , 


Sample  No.  27.— Pasteurized  Milk  Kept  at  20°  C. 


Total  bacteria  . . . 

Total  lactic 

Total  liquefiers.. 
Rapid  liquefiers. 
Slow  liquefiers  .. 
Inert 


Total  bacteria... 

Total  lactic 

Total  liquefiers.. 
Rapid  liquefiers . 
Slow  liquefiers... 
Inert 


2, 220 


7.5,500 

72, 920 

280 


280 
300 


15, 650, 000 

15, 552,  .500 

30,000 


30,000 
67,  .500 


1,227,500,000. 

1,218,2.50.000, 

760,000, 

.500, 000. . 

250,000,. 

7,  .500, 000  . 


Sample  No.  37.— Pasteurized  Milk  Kept  at  10° C. 

2,220  2,H(10  2,350  3,130  :'6,500'     6,715,000 


0 


10 


10 


120|  70,000 

90; 

30: 

36,3801    6,645,000 


BACTERIA    OF    PASTP:URIZED    AND    UNPASTEURIZED    MILK.       21 

Table  V. — Bacteria  per  cubic  centimeter  of  milk,  arranged  in  groups — Continued. 
Sample  No.  18.— Raw  iMiLK  Kept  at  10°  C. 


Group. 


Number  of  bacteria  found  after  lapse  of- 


0  hours.       6  hours.      V2  hours.       24  hours.        48  hours. 


72  hours.      %  hours. 


Total  bacteria 2,600,0001    g.ST.i.OlKi  24,2.tO,00«i 

Total  lactic 2,  125, 0001    H,  ti;5.^,  OOi)   22, 700, 000' 

Totallifiueners...         12.5,000  " " 


Rapid  li<iucfiers  .. 

Slow  liriuetiers 

Inert 


2.5,0001 
100,000 
;'0,(H0 


800,000, 
575,000 
225,  tKX)l 
1.50,  OOO! 


l,22o,000| 
775, 000 1 
•1.5t),  (KJO 
;{2.5, 000 


.5H,  .500,  000 
.52,  .500, 000 
5,7.')O,00O; 
3,  .500, 000 
2, 2.50,  (HX) 
1,2.50,000 


1.H9,  .500,0(.)0  191,  .500,000 
1K3,.500,(X)0 

4,.500,000, 

l,.500,000i 

3,  (KX),  (XX)i 

1,.')00.000 


•Sample  No.  2k.— rASTEfiu/.ED  Milk  Keit  at  20°  (\ 


21.5,5UU,(<a) 

189,700,000 

1,800.1X10 

1 ,  175.  (XK) 

325, 000 


Total  bacteria 

80 

.so 

420 

Uft.lXX) 

y,loo,o(X)' 

Total  lactic 

Toljil  li(HU'tiers... 
Rapid  liiiiiclicrs  .. 

0 
0 

10 
10 

-90 
170 
l-'O 

75,  (XX) 
.^5,000 
20,000 

87.5,  (XX) 

12.5.000 

4.".(),(XX) 

Inert 

i 

, 

1                       1 

lA.MIM.E    No.  UK,  — I'ASTEIKl/.En   MlI.K    KEIT   AT    10°  ('. 


Total  bacteria 

Total  lactic 

81) 

00 

10 

10 

70 

S,  .500 

.532.  'i.%) 

Total  li(|iicliers. . . 

0 

0 

0 

0 

10 
10 

7'XI 
7."X)  . . . 

0 

Inert ... 

7.760 

■  3 '  .500 

Sample  No.  H».— Raw  .Milk  Keit  at  20"  c 


Total  bactiTia  ...  10,287, .5<X)  " '.i, .■,()(), (KX) 

Total  laclic lu,()t)2, .5tHl 

ToImI  lii|iiclicrs...  17-5,  (KX) 

Kiipid  liinirficrs  ..  75, (KK) 

Slow  li(iiiclicrs Kio.lKMi 

Inert rx).(KX), 


<") 


IO.S75,UOO       93,fi(X),(K)0 
■10,  .5.50,  tXX)       y3,.'>0l),(KH)  , 
2'.'.5,0(X)!  .50,(100 

UK),IK)0  .50,(HHI 

125,000 

UK),  IHKl  .'>(),  (KM), 


-I'A.sTKiitizEii  Milk   Kipt  ai'  20"  c 


'I'otal  bacteria  . 

Total  laeti<' 

Total  lii|iiclicrs 
Rapid  li(|Oi'li('i> 
.Slow  li(|Uflicrs. 
Inert 


110 
110 


v\Ml  1  K    No.  :!'.!. —  r\sTKIHlZKI>    MlIK     KEPT   AT    10  '  (' 


Total  bacteria 
Total  lactic... 


Totiil  liiiuclicrs. . . 
Rapid  li(|nelicis  . . 
Slow  licpicticr^. . . . 
Inert 


Dilntioii  loo  liiKli. 


22 


BUREAU    OF    ANIMAL    INDUSTRY. 


Table  W.  — Bacteria  per  cubic  centimeter  of  mUk,  arranged  in  groups — Continued. 

Sample  No.  110.— Raw  Milk  Kejt  at  10°  C. 


Gronp. 

Number  erf  bacteria  found  after  lapse  of— 

Ohoun. 

6  hours. 

12  houni. 

24  hoars. 

48  hours. 

72  hours. 

96  hours. 

Total  bacteria 

Total  lactic 

Total  liquefiers... 
Rapid  liqnoflcrs . . 

Slow  liquefiers 

Inert 

252.500 
185,000 
67,500 
40,000 
27,500 

1,082,  ,500 

mi,  500 

210.000 

132,  .500 

77,500 

10,000 

8,200.000 
5,(iOO,0(K) 
2,  .575, 000 
1,225,000 
1,350,000 
25,000 

57,000,000 
40,040,000 
15, 9<i0, 0(X) 

5, 210, 000 
10,750,000 

1,000,000 

211,250,000 

181,375.000 

26. 875.  (XH) 

19,87.5,000 

7,000.000 

3,000,000 

5.37.000.000 
51  ti.  .5.50.  (XX) 
I(>, ".')(),  000 
10,000,000 
(•>,  7.50, 000 
3,700,000 

661. 2.50,  (XX) 
637,  axi,  (XX) 
19.2ri0,000 
13, 17,5,  (XX) 
6,125,000 
5,000,000 

Sample  No.  210.— Pasteurized  Milk  Kept  at  20°  C. 

Total  bacteria 

40 

60 

40 

IBO 

a7,500 

Total  lactic 

Totjil  liqu<'flers... 

0 

20 
20 

10 
10 

150 
150 

2,  .500 
2,500 

Rapid  liquefiers . . 

Sample  No.  310.— Pasteukized  Milk  Kept  at  10°  C. 


Total  bacteria 

Total  lactic 

40 

30 

3b 

40 

30 

200 

2,800 

Total  liquefiers... 

0 

10 

6 
5 

30 
20 
10 

150 
.1.50 

2,800 

10 

2,800 

Inert 

Sample  No.  ill.— Raw  Milk  Kept  at  20°  C. 


Total  bacteria 

Total  lactic 

Total  liquefiers... 
Rapid  liquefiers  . . 

Slow  liquefiers 

Inert 


7,050,000 
d.  847, 500 
180, 000 
20,000 
160,000 
22,  .500 


106,  -450,  (KX) 
105, 300,  (XK) 
825, 000 
175,000 
6.50,000 
325, 000 


229, 437,  ,500 

225, 187,  .500 

3,.5(X),000 

:k)0,  000 

3, 000. 000 

750,000 


.543, 000, 000 

.540, 7.50,  (XX) 

2, 000, 000 

625, 000 

1,37.5,000 

250,000 


799,  .500, 000' 

799, 300, 000  . 

12.5,0001. 


12.5,0001. 
75,000,, 


Sample  No.  211.— Pasteikizeo  Mii.k   Kkpt  at  20°  C. 


Total  bacteria 

Total  lactic 

Total  liquefiers.. 
Rapid  liquefiers  . 
Slow  liquefiers... 
Inert - 


835 


35 

10 

25 

800 


185 


:!8,7(X)'  ('') 

3(i,90t)i 

1 ,  100'  397,  .500 

22,  .500 

1,400            37.5,000 
400 


Sample  No.  311.— Pa.steckized  .Milk  Kept  at  10°  C 


Total  bacteria  — 
Total  lactic 

70 

95 

1,000 

920                1,630 

273, 900 

273,000 

900 

300. 

600 

2.5,920.0(X) 
25,917.900 

Total  li(|uefiers 

20 

20 

20 

25 

10 

2  IIX) 

Rapid  liquefiers .. 

10 

20 

25 

2,  KX) 

aDilutioii  too  hif?h. 


ftDilutiou  too  low. 


BACTERIA    OF    PASTEURIZED    AND    UNPASTEURIZED    MILK.      23 

T.vBLE  V. — Bacterid  per  cubic  centimeter  of  milk,  arramjed  in  (/roups — Continued. 
Sample  No.  112.— Raw  Milk  Kbit  at  10°  C. 


Group. 

Number  of  bacti-ria  found  after  lapse  of— 

0  hours. 

6  hours.      12  hours.       24  hours. 

48  hours.       72  hours.       96  hours. 

Total  bacU'ria 

21 7,. TOO 
170,000 
32,500 
12,500 
20,000 
15,000 

96.5,000     3,012,500       25, 462,  .500 
900, 000     2, 587. 500       23, 1  ti2,  .500 
.52,500         3-2.5,000         1,950,000 
12,  .500          75, 000            .500.  (KX) 
10,000         250, 0(X)         1,4.50,000 
12,500         100.000            :?50,(XX) 

1.5.5, 812,  .500  221,  .500. 000 

Totiil  lactic 

Total  li(|iU'lk'n> 

144.247,-500 

3,690,0<X)    11,000,000 

Rapid  li(iiictifrs  .. 

375.  (HIO 

3,:{.')0.000          

Inert 

7, 875, 000 

SaMIM.K   No.  212.  — I'A.STKIHI/.KI)    MiLK    K  KIT   AT  20"  (' 


Total  bacteria.. 

Total  lactic 

Total  li(iiie(iers. 
Rapid  licpieliers 
Slow  liquetiers.. 
Inert 


1.481,800  . 


195  1.184.800. 

195  1.484.800. 


Sa.mi'LK.  No.  312.— I'a.stkikizkh  Milk   Kktt  at  10°  (' 


Total  bacteria 

Total  lactic 

192 

132 

12 

no 

110 

•V).  (i<KI 

Total  li(|ncfier.>i . . . 

^'• 

15 
10 

0 

.-, 

■50 

~ 



.50 

5 



Inert L . 

.55,  .").')0    

Sami'i.k  No.  113.— Raw  Milk   Keit  at  20°  C. 


Total  bacteria  . 

Total  lactic 

Total  li<iliefiers 
Rapiil  li(iui'fiers 
Slow  li(me(iers 
Itiert 


1 .  .SO-i,  :M)  1.57.  437,  .500  (ii'.t.  IKMt,  000  1 .  181 ,  ;5(H).  (XHt  . 

1 .  77t;,  7.VJ  1.55,  137.  .5(KI  628.  (HH).  (HH)  1 ,  180,  925.  (KK)  . 

20.  IKK)  9.')0,(HKI  125,  (KHI  275. 0(K). 

T-'iO  l.'HI.IKMI  75.  (KK) 

|y,2.'i<l  .-^IHI.iMKt  :UI.(KH)  275,0(10. 

5. 7.'>0       1,050.  (HKl  .575.  (KM)  3(KI,  (KM), 


Sa.MI'I.K    N<i.  213.    -I'ASTLI   I'.IZKIi    .Mll.K     KKIT    AT    20'     (' 


Total  biicicri 
Total  laili 
Tiital  lii|iii 
Rapid  lii|iieticrN  - 
.^low  lii|iielicrs. . . 
Inert 


rill 

12(1 

8  15 

.".(HI 

1.051 

,  0(XI 

13,  (IT.' 

,(XHI 1 

icrs... 

10 

25 

."^Ml 

1,1151 

,0(HI 

13,07.- 

.(KHI 1 

-I'A.-^^I  KIIIIZKIi    Mll.K     KKI-I     at    Kf     C. 


Total  bacteria  . . . 

Total  lactic 

Total  li.jiiclicrs.. 
|{api<l  lii|Uclier.'^i. 
Slow  lii|iictiers.  . . 


;;.m; 

■.t.'XI 

ii.ii;r 

.."i<HI 

J.5II 

■^:*  1 

.  J.'HI 
.  2.'>0 

3"M'| 

7(HI 

11,  (« 

.2.-HI 

24 


BUREAU  OK  ANIMAL  INDUSTRY. 


Table  V. — Bacteria  per  cubic  centimeter  of  milk,  arranged  in  groups — Continued. 
Sample  No.  114.— Raw  Milk  Kept  at  VP  C.    ' 


Group. 

Number  of  bacteria  found  after  lapse  of— 

0  hours. 

6  hours. 

12  hours. 

24  hours. 

48  hours. 

72  hours. 

96  hours. 

Total  bacteria .... 

38,000 

33,250 

3,250 

2,500 

750 

1,500 

260,000 

202,500 

50,000 

45,000 

6,000 

7,500 

3,026,000 

2,726,000 

226,000 

226,000 

27.687,500 

25,862,500 

1,600,000 

1.600.000 

313,000,000 
305, 125, 000 

Total  lactic 

Total  liquetiers... 

12,500 
12,500 

5,375,000 
3,750,000 
1,626,000 
2,500,000 

Rapid  liquefiers.. 

Slow  liquefiers  ... 
Inert 

75,  OOol            22.5. 666 

Sample  No.  214.— Pasteueizkd  Milk  Kept  at  20°  C. 


122 

50 

520 

26,000 

1,276,000 

Tot»il  lactic        .  . 

Total  liquefiers 

10 
10 

10 
10 

460 
460 

25,666 
25,000 

1,276,000 
1,275,000 

Rapid  liquefiers . . 

Sample  No.  314.— Pasteurized  Milk  Kept  at  10°  C. 


Total  bacteria 

122 

60 

40 

380 

2,000 

54, 255, 000 

Total  lactic 

Total  liquefiers . . . 
Rapid  liquefiers . . 
Slow  liquefiers 

10 
10 

10 
10 

10 
10 

16 
16 

10 
10 

100 
100 

4,000 
4,000 

370 

1,900 

54,261,000 

T.\BLE  VI. — Average  number  of  bacteria  per  cubic  centimeter  in  all  samples  under  each 

treatment. 


Description    and    treat- 
ment of  sample. 


Number  of  bacteria  after  the  lapse  of- 


0  hours.  !  6  hours.     12  hours.     24  hours.     48  hours.     72  hours.     96  hours. 


Raw  milk  kept  at  20°  C. . . 
Pasteurized  milk  kept  at 

20°C 

Raw  milk  kept  at  10° C. . . 
Pa.steurized  milk  kept  at 

10°C 


13, 522, 331|74, 142, 857  247, 651, 250 

246  426  6,028 

17,640,428  31,457,833   38,406,785 


308 


457, 910, 714;608, 079, 166  568, 718,  .tOO 


1, 501, 3a5  3-20, 337, 388  236, 941 , 2.50  975, 500, 000 
308, 041 ,  666  5(;2, 650, 000 


124, 783, 928,254, 678, 542 

I 
1,026     15,119 


2,462,492  37,088,456 


Probably  the  most  striking  thing  in  these  tables,  especially  to  the 
person  not  familar  with  the  bacteriology  of  milk,  is  the  enormous 
number  of  bacteria  usualh'  found  in  the  raw  milk  after  standing  two 
or  three  days.  This  number  always  reached  several  hundred  million 
per  cubic  centimeter,  and  occasionally  went  as  high  as  1,000,000,000. 
Even  higher  numbers  have  been  obtained  ('*). 

Accepting  Cohn's  ('")  calculation  of  the  weight  of  a  single  bacillus 
as  0.000,000,001,571  milligi-am,  the  weight  of  1,000,000,000  bacteria, 
a  number  not  infrequently  found  in  a  cubic  centimeter  of  milk,  would 
be  over  1^  milligrams.  In  other  words,  over  i^  tenths  of  1  per  cent 
of  the  total  weight  of  the  milk  has  been  converted  into  plant  tissue. 
But  even  this  does  not  tell  the  whole  truth.  In  the  course  of  their 
growth  the  bacteria  have  converted  a  considerable  proportion  of  the 


BACTERIA    OF    PASTEURIZED    AND    UNPASTEURIZED    MILK,       25 

milk  solids  into  l)y-products  of  j^rowth.  If,  as  is  usually  the  case, 
when  such  larj^e  numbers  are  found,  the  bacteria  are  of  the  lactic- 
acid  class,  the  decomposition  is  of  a  comparatively  harmless  nature, 
although  in  each  cubic  centimeter  of  milk  5.7  millij^rams  of  lactose 
may  have  been  converted  into  ♦{  milligrams  of  lactic  acid;  on  the 
other  hand,  if  many  bacteria  of  the  liquefying  group  are  present,  each 
tiny  cell,  by  secreting  its  digestive  enzymes,  minute  in  the  individual 
but  potentially  great  in  the  aggregate,  is  al)le  to  produce  results  all 
out  of  proportion  to  its  infinitesimal  weight. 

The  inliuence  of  low  temperatures  in  retarding  the  growth  of  bac- 
teria is  well  known,  but  it  may  be  of  interest  to  compare  the  increase 
under  the  conditions  of  this  experiment.  In  considering  the  multipli- 
cation of  a  single  cell  in  the  raw  milk,  it  should  be  remembered  that 
at  the  time  the  count  began  the  bacteria  had  already  passed  the  period 
of  rapid  increase.  For  this  reason  the  increase  of  the  bacteria  in  the 
pasteuriz(>d  milk,  as  tabulated  in  Tal)le  VII,  can  not  be  compared  with 
the  increase  in  the  raw  milk  under  similar  conditions. 

Taki.e  \'I1.  —  lucreuxi'  <>/ a  kiik/i  '  fxniciniin  in  mn'  rahif  mitiiiu'ter  i>f  milk. 


DesiTiptidii  iiiid  treiitini'iu 
of  Siiniplc. 


NumlnTol"  Iiiictcriii  t'ouiKi  al'tiT  tlu'  lapse  of— 
(I  hours.     tiliiHirs.     I'i  hours.   'Jl  liours.      is  hours.     72  hours.     Wi  liours. 


Raw  milk  lit -JO"  (■ ,  \\  .'»..'>  l.H.:;            :«.*)                ii.it  1J..'>    

Kiiw  milk  at  ID'C I  Ij  1.7  I  2.  J              7.1                 11.1  17.4  ai.l 

I'astvuri/iMl  milk  at 'JO^C  ..  li  1.7  Jl.J  i..  l'>  S(i7.  I'.f.i  '.tf.7. 107  ;;. '.tM.r,;!.' 

I'astiMirizcMi  milk  at  HFC  ..  l'  1.2  1  1.;'.               1.1                  (1.2  Hi,(i:>l  li:{,21,s 

It  will  l)e  seen  that  the  progeny  of  a  single  cell  in  the  raw  milk  htdd 
at  10  C\  had  not  rc^acluHl  in  '.Hi  jiours  the  numbei-  attained  in  the  raw 
milk  at  l^o  ('.  in  "24  houi's.  In  the  j)asteurized  milU"  the  conditions 
ar(>  different  in  that  the  count  beginning  when  the  milk  contained  a 
\erv  few  t»acteria  only  extends  over  the  jHM'itxi  of  rapid  increase.  The 
Itacteiial  multiplication  was  very  rai)id  in  the  pa>teiiri/.e(i  milk  held 
at  20"  C'..  a  single  organism  i'ej)ro(lucing  itself  three  hundred  thousand 
times  in  4>i  hoiiis.  'i'he  pasteurized  milk  held  at  10  ('.  i)i'e^eiit>  a 
stiiking  (.•outlast:  the  multiplication  was  xciy  slow  tOr  the  lii'^t  4^ 
hours,  and  at  the  end  of  !'<;  hours  the  iricreas(>  was  f;ir  below  that  in 
the  pasteurized  milk  at  the  higher  teniperatui-e. 

Keturning  to  the  actual  iiiiiiibers  of  l>acteria  in  the  milk  we  lind  that 
at  the  time  of  pasteurization  the  mean  of  the  s:imj)les  held  at  2o  (". 
was  i;^),oo(».M0O  |)er  cubic  centimelei-.  while  the  milk  held  at  Jo  ('. 
shows  a  slightly  higher  niimlx'i'.  This  pi'obably  i-eproeiits  pdor  rather 
than  average  city  milk,  but  may  be  taken  as  a  fair  saiii|)le  of  milk 
lUMMling  pasteurization.  The  i-etluction  of  this  number  to  l'I.'*  per  cnl»ic 
centimeter  may    be  considered  as  ellicient    pastcuri/at  ion.  ])roltat>ly  a 


26  BUREAU  OF  ANIMAL  INDUSTRY. 

higher  efficiency  than  would  be  obtained  under  ordinary  commercial 
conditions.  The  variation  from  the  mean  was  slight;  the  minim uin 
number  found  was  20  per  cubic  centimeter  and  the  maximum  4,040. 
The  latter  was  so  exceptional  that  the  results  from  this  sample  (No. 
33)  were  excluded  in  making  up  the  means. 

Milk  under  ordinary  conditions  is  held  in  a  refrigerator  at  10-^  to 
IS'^  C.  and  is  consumed  usually  within  12  hours  or  at  most  24  hours 
after  delivery.  The  milk  held  at  10^  C.  will  therefore  represent 
normal  conditions  more  nearly  tlian  that  held  at  20^  C,  but  it  will  be 
of  interest  to  study  the  bacterial  development  in  the  milk  held  at  the 
higher  temperature. 

In  the  raw  milk  over  200,000,000  bacteria  per  cubic  centimeter 
were  found  at  12  hours,  while  the  same  quantity  of  pasteurized  milk 
contained  about  6,000  onl}';  12  hours  later  the  latter  number  had 
increased  to  over  1,000,000,  and  at  48  hours  the  diflerence  in  the  total 
bacteria  present  In  the  two  cases  was  small.  There  is  more  or  less 
variation  from  these  means  in  individual  cases,  but  the  frequency  of 
their  occurrence  makes  it  safe  to  predict  that  pasteurized  milk  held  at 
20°  C.  for  24  hours  or  more  will  have  a  high  bacterial  content. 

The  growth  of  bacteria  in  the  pasteurized  milk  at  the  low  tempera- 
ture is  so  slow  that  at  48  hours  after  pasteurization  the  number  of 
bacteria  was  less  than  that  usually  found  in  sanitary  milk,  and  oven 
at  96  hours  was  not  much  greater  than  the  total  number  in  the  milk 
before  it  was  heated.  The  results  obtained  at  this  teniperature  were 
uniform,  showing  much  variation  at  72  hours  and  96  hours  only.  At 
these  two  periods  two  or  three  exceptionally  high  results  have  raised 
the  general  mean  considerably  above  that  of  the  remaining  counts. 

Milk  showing  an  acidity  of  about  0.25  per  cent  has  a  distinct  sour 
taste,  and  would  not  be  considered  fit  for  use  after  it  had  reached  this 
condition.  The  average  raw  milk  had  reached  this  stage  at  48  hours, 
while  the  pasteurized  milk  was,  so  far  as  the  total  bacteria  show,  in 
good  condition  24  and  even  48  hours  later.  At  20*-^  the  diti'erence  was 
somewhat  less  although,  as  will  be  pointed  out  later,  the  nature  of  the 
bacteria  developing  in  the  pasteurized  milk  at  the  higher  temperature 
has  some  influence  on  the  length  of  time  during  which  it  may  be  con- 
sidered fit  for  use. 

It  is,  however,  verv  unsafe  to  judge  the  quality  of  the  milk  by  the 
total  number  of  bacteria  present  without  regard  to  their  nature.  A 
few  hundred  thousand  l)acteria  of  certain  species  may  be  more  harm- 
ful than  a  hundred  million  of  another  class.  For  this  reason  it  will 
be  more  profitable  to  consider  the  bacteria  grouped  under  the  head  of 
peptor)iziiig  l)acteria,  as  this  group  includes  the  bacteria  generally 
acknowledged  to  be  the  cause  of  the  most  undesirable  changes  in  the 
milk.  It  is  difficult  to  secure  accurate  counts  of  li(iuefving  l)acteiia, 
especially  when  they  are  growing  with  lactic-acid   bactei-ia,  but  the 


BACTERIA    OF    PASTEURIZED    AND    UNPASTEURIZED   MILK.       27 


results  given  in  Table  VIJI  nmy  be  taken  as  a  fair  representation  of 
the  growth  of  this  group  under  these  conditions. 

Tahle  VIII. — Areraye  number  of  peplonizing  bacteria  per  cubic  centimeter  of  milk. 


Description  and  treatment 
of  sample. 


Raw  milk  at  '20°  C 

Pasteurized  milk  at  2()°  C. . 

Raw  milk  at  10°  C 

Pasteurized  milk  at  10°  C. 


Number  of  bacteria  found  after  the  lap.se  of— 
0  hours,     (i  hours.  !  12  hours.  I  24  hours.  I  48  hours.     72  hours.  1  96  hours. 


iVZlJul    4,905,3:« 


82,20H       50.0,333 
7  11 


1,  H14,  .tK3  2, 927,  H57         700,  OOO'     1, 375, 000 

188       2o9,831j    2,411, 1(;3   31,225,000 

I,518,6<i6'  5,272,500  ll,70a,7.'iO   12,781,2r«32,918,7.T0 

y,               15;  3,143;       ♦v56,219   4,251,219 


In  making  up  the  mean  for  the  raw  milk  at  20  C.  those  determina- 
tions in  which  .^omc  unusual  circumstance  made  the  count  evidently 
inaccurate  are  not  included.  In  this  milk  the  mean  shows  a  rapid 
increases  of  licjuefving  bacteria  for  the  first  <!  hours,  followed  l)y  a 
gra(Uial  decline.  In  the  samples  held  at  room  temperature,  which  at 
the  time  this  work  was  done  was  usually  below  2(>  C,  the  maximum 
was  reached  in  all  cases  at  24  hours,  but  a  few  high  numbers  in  the 
later  samples  htdd  at  20"^  C^.  bring  the  mean  maximum  down  to  6 
hours.  The  variation  in  the  actual  number  of  peptonizing  bactei'ia 
present  in  the  dirt'erent  .samj^les  was  large,  ranging  from  a  fcnv  thou.sand 
to  24:,(K)0.<H)0  per  cubic  centimeter. 

In  the  pasttnirized  milk  lu^ld  at  '20  ('.  the  peptonizing  bactei-ia, 
freed  from  the  inhibiting  inHuence  of  the  lactic  group,  increased 
uniformly.  The  av«Ma<>e  number  found  at  24  hours  was  a  little  oNcr 
200,0(10  pel'  cubic  centimeter,  increasing  to  onim'  'J.OOO.OOO  at  4S  hours 
and  to  80,0(»0.000  at  72  hours.  The  number  pr(>.sent  during  the  tirst 
12  hours  was  insigniticant.  There  is  considerable  variation  at  this 
temperature  and  more  or  less  inaccuracy,  owing  to  the  dillicuhy  in 
securing  a  correct  count  of  a  large  numb(>r  of  rapid  ruiuetiers. 

In  tiu^  i-aw  milk  held  at  10  C.  the  multiplication  of  li(|uetieis  was 
less  rapid,  but  continued  for  a  longei-  period,  and  reached  in  one  case 
(sample  No.  Ml)  !»lt,ooo.ooo  in  !»<;  hours,  although  the  lactic  bacteria 
were  present  in  lai'ge  numt)ers  from  the  beginning.  An  examination 
of  Table  III  shows  that  the  acidity  of  this  milk  at  1M>  hours  was  o.-_':> 
pel"  cent  only,  which  is  a  little  below  the  mean  for  4S  houi's.  Kxclud- 
ing  this  excej)tionally  high  ligun*  th(>  mean  number  of  litiuelieis  j)res- 
ent  at  iMi  hours  would  be  jo. SHI  JUJti.  indicating  a  slight  falling  oil  after 
72  hours. 

The  counts  of  the  Ii(|Uefying  bacteria  in  the  pasteurized  milk  at   b» 
C    indicate   that    there   was  scarcely   any    growth    for    IS   hours,   and 
even  aft(M'  tH>  hours  the  nunilxM'  found  was  no  greater  than  that  of  the 
unh(>ated  milk  72  lioiiis  earlier.      In  other  words,  the  pasteurized  milk 
was  m  better  condition,  so  far  as  bacteriological  examination  shows. 


28  BUREAU    OK    ANIMAL   INDUSTRY. 

flti-  when  48  hours  old  than  the  unheated  milk  at  the  time  of  pasteuriza- 
tion.    In  many  cases  there  were  very  few  licjuetiers  even  at  9H  hours. 

The  variation  in  species  occurring  in  these  samples  of  milk  was  not 
great.  Three  or  four  species  of  liquefiers  were  almost  uniformly 
present  and  all  nuiltiplied  more  or  less,  although,  after  the  influence 
of  the  lactic-acid  bacteria  began  to  be  felt,  this  number  was  usually 
reduced  to  one  or  two  varieties.  The  most  common  and  persistent  of 
these  was  the  hay  bacillus. 

Two  or  three  species  of  liquefiers  usually  survived  pasteurization. 
In  the  hearted  milk  held  at  20°  C,  the'  great  increase  was  confined, 
almost  without  exception,  to  the  hay  bacillus.  The  rapid  growth  of 
the  colonies  of  this  organism  usually  prevented  the  determination  of 
the  slower  growing,  less  abundant  species. 

The  hay  bacillus  developed  much  more  slowly  in  the  pasteurized 
milk  at  10^  C.  For  this  reason  it  was  possible  to  ascertain  the 
presence  of  a  few  other  species,  none  of  which  could  be  called 
predominant. 

The  ba(^teria  included  under  the  heading  "inert"  were  mostly  of  a 
group  forming  white  colonies  spreading  slightly  on  the  surface  of  the 
gelatin.  In  the  pasteurized  milk,  however,  and  especially  the  part 
held  at  10^  C,  there  frequently  occurred  a  considerable  increase  of  a 
variety  forming  small  round  colonies  resembling  the  colonies  of  the 
lactic  group,  but  without  appreciable  effect  on  milk.  The  lactic-acid 
bacteria  which  survived  pasteurization  were  found,  in  nearly  every 
case,  to  be  identical  with  the  predominating  lactic  species  in  the  cor- 
responding unheated  milk. 

The  qualitative  difference  in  the  flora  of  the  pasteurized  and  unpas- 
teurized milk  consisted  in  the  absence,  with  a  few  exceptions,  of  the 
lactic  group  from  the  latter,  the  small  reduction  in  the  number  of 
varieties  of  peptonizing  bacteria,  the  rapid  nuiltiplication  of  the  hay 
bacillus  in  the  heated  milk  at  20°  C,  and  the  presence  in  some  cases 
o*f  large  numbers  of  inert  bacteria  in  the  pasteurized  milk  held  at 
20- C. 

INFLUENCE  OF  LACTIC  BACTERIA  ON  THE  DEVELOPMENT  OF  PEPTONIZ- 
ING BACTERIA. 

Taking  up  the  question  of  the  protective  action  of  the  lactic  group, 
we  find  that  when  both  the  lactic  and  the  peptonizing  bacteria  are 
growing  together  in  milk,  as  in  the  unheated  milk  in  these  experiments, 
there  was  a  rapid  increase  in  tlie  latter  for  a  sliort  time,  followed  by  a 
period  of  slow  decrease,  or  at  least  a  complete  prevention  of  nuiltij)li- 
cation.  This  was  not  confined  to  a  single  species,  but  included  all 
li(iuefiers  found  in  these  milks.  Reference  to  Table  IX  shows  that 
this  inhibition  was  coincident  with  the  development  of  from  0.25  per 
cent  to  0.3  per  cent  acidity: 


BACTERIA    OF    PASTEURIZED    AND    UNPASTEURIZED    MILK.       29 


Tablk  IX. — Relaiion  of  aciditij  of  milk  to  development  of  peptonizing  hacteria. 


Percentage  of  acidity  and  number  of  bacteria  after  the  lapse  of — 

0  hours. 

.131 

621,577 
.138 

6  hours.  '  12  hours.  24  hours. 

48  hours. 

72  hours. 

%  hours. 

(Acuditv 

.168             .254             .449 

4,9a5,333   1,814,.->H.3   2,927,000 

.153  1           .168             .183 

30<i,4OO  ,l.W2,40O  i5, 827, 000 

1                    1 

.696 

700, 0(X) 

.  245 

9, 200. 500 

.711 
1,. 37.5, 000 

.417 
12,781,2.50 

20° 

Pcptniii/iiif;  iHictoria 

f.\ci<litv 

.  551 

10°        •.  : 

PeplonizinK  bactonii 

73,  (WH* 

10,891,r*6 

In  the  raw  milk  at  20*^  C.,  tho  j^rowth  of  the  liquofiors  wa.s  checked 
between  ♦!  hours  and  12  hours;  in  this  period  the  acidity  increased 
from  0. 16H  per  cent  to  0.254  per  cent.  In  the  raw  milk  at  10  C,  the 
continued  deveh)pment  of  the  li(|uefiers  was  proportionate  to  i\w  slow 
increase  in  the  acidity.  If  we  exclude  No.  HJ,  which,  as  has  alieady 
been  explained,  showed  an  exceptionally  slow  increase  in  acidity,  thcM-e 
was  little  increase  after  4S  hours,  when  the  acidity  had  reached  <».245 
per  cent.  Thi*  samples  (Nos.  21,  22,  2(5,  and  27)  in  which  there  was  a 
sudden  multiplication  of  lactic-acid  bacteria,  with  a  correspond! nj^ly 
increased  acidity  in  the  pasteurized  milk,  were  accompanied  by  a  sharp 
decrease  in  the  li((uefyin^  l)acteria. 

Bouska,  ('")  who  has  done  some  extensive  work  alon<if  this  line, 
states  that,  while  the  major  part  of  the  inhibitory  action  exercised  t)y 
the  lactic  bacteria  on  B.  suhfl/is  is  due  to  lactic  acid,  it  is  also  evident 
in  media  containinjjf  no  suj^ar. 

Thus  it  seems  evich'iit  that  the  protective  inHuence  of  the  lactic 
t^roup  of  l)act(M'ia  becomes  ertectiv<»  only  when  the  acidity  hiis  n^ached 
a  point  that  renders  the  mill<  uiuh^sirable  for  food.  The  tables  oi\en 
in  the  [)a[)er  by  Conn  and  Ksteii.  ('')  j)reviously  ([uoted,  show  a  more 
or  less  rapid  increase  of  li(|uetiei's  for  a  time,  depeiurm*^"  on  the  tem- 
perature at  which  the  milk  was  held.  Althoutjfh  the  acidity  is  not 
j^iven,  the  number  of  lactic  bacteria  present  makes  it  j)robable  that 
the  li(iuefiers  increased  until  the  milk  was  at  least  sliohtly  sour. 

This  ai)))lie.u  liowevtM".  to  the  numl)er  of  liciuetiers  prestMit,  and  does 
not  take  into  account  the  eti'ect  of  the  acid  reaction  on  the  proteolytic 
en/ymes  seci'cted  by  this  trroup  of  l>acteria.  The  |)asteuii/,ed  milk 
held  at  2<>  ('.  fretiuently  cui(11(h1  is  hours  aftei-  pasteurization,  with  a 
very  di.sa«ireeable  taste,  althouuh  the  m«'aii  luimber  of  peptoiiizintjf 
l>acteria  found  at  this  time  was  only  "J.^dO.ooo  |)ei'  cubic  centimeter, 
while  the  raw  milk  containinu-  seMMui  times  as  many  l>acteria  of  this 
«iroup.  in  addition  to  the  lactic  l)acteria.  u^umIIv  remained  unchaiiLi'ed 
except  for  a  slight  soiii' taste.  It  must  be  reinemlxMed.  lio\\«'\  tM".  that 
tlu'  acidity  was  sullicient  to  obscure  any  clian^e  e\ce|)t  a  decidiMl  one. 

In  one  instance  (sample  No.  hi),  in  which  the  I'aw  milk  contaiiiiMl 
«>!>, 000, ()(»(»  peptoniziu.u'  bjicteiia  per  cul»ic  centimeter,  t  h(^s(>  bacteria 
had  not  appreciably  atl'ected  the  taste.  In  \  iew  of  the  ti'yjjtic  nature 
of  the  bacterial  proteolytic  enzynicvs  and  the  well-known  sensiti\ fuess 


30  BUREAU    OF    ANIMAL    INDUSTRY. 

of  this  enzyme  to  acid  reactions,  it  is  probable  that  the  acid  produced 
by  the  lactic  bacteria  has  a  very  distinct  inhibiting"  eflFect  on  the  bac- 
terial enzymes  in  milk  and  that  their  protective  value  is  due  to  this 
fact  rather  than  to  their  retarding  influence  on  the  growth  of  the 
organism  itself.  That  this  action  is  not  entirely  eflfective  is  shown  by 
some  of  the  work  cited  in  the  introduction  to  this  paper. 

CONCLUSIONS. 

With  the  conditions  under  which  this  investigation  was  carried  on, 
milk  held  at  10'^  C.  was  found  to  be  in  good  condition  from  a  bacterio- 
logical standpoint  for  48  hours  after  pasteurization.  The  same  milk 
if  held  at  20°  C.  could  not  be  considered  a  safe  food  longer  than  24 
hours  after  pasteurization.  The  presence  of  a  large  number  of  pep- 
tonizing bacteria  in  the  pasteurized  milk  usuall}'^  caused  such  a  marked 
change  in  the  taste  that  it  would  not  be  used  after  these  organisms  had 
become  very  numerous.  The  bacteria  of  this  class  were  frequently 
found  in  the  raw  milk  and  were  found  especially  in  the  raw  milk  held 
at  the  lower  temperature  in  greater  numbers  than  in  the  pasteurized 
milk  under  similar  conditions,  but  some  influence,  evidently  the  acid, 
so  retarded  their  activity  that  they  usually  did  not  appreciabl}^  aflfect 
the  taste  of  the  milk. 

Inasmuch,  however,  as  the  present  experiments  were  carried  on  in 
a  laboratory  under  carefully  controlled  conditions,  it  would  be  unsafe 
to  apply  the  same  deductions  to  pasteurization  on  a  commercial  scale. 
If  milk  could  be  pasteurized  commercially  in  such  a  way  that  the  bac- 
teria would  be  reduced  to  a  few  hundred  per  cubic  centimeter  and 
held  at  a  low  temperature  until  used,  it  would  be  perfectly  safe  for  48 
hours  or  even  72  hours.  Under  these  circumstances  it  would  probably 
be  in  better  condition  after  this  long  period  than  ordinar}-  city  milk 
at  the  time  it  is  delivered.  How  closely  these  conditions  could  be 
approximated  commercially  is  another  question. 

SUMMARY. 

Briefly  summarized,  the  facts  brought  out  in  the  first  portion  of  this 
paper  are  as  follows: 

Examination  of  milk  by  many  bacteriologists  shows  that  the  milk 
used  in  American  cities  is  usualh'  badly  contaminated  by  bacteria. 

Increased  public  interest  in  the  milk  supply  has  ivsulted  in  more 
rigid  municipal  regulations  and  inspection,  but  progress  is  necessarily 
slow  and  pasteurization  is  fivcjuontly  resorted  to  in  order  to  increase 
the  length  of  time  that  the  milk  will  remain  sweet  and  to  reduce  the 
danger  from  spread  of  infectious  diseases. 

The  objection  is  frequentl}'  made  that  pasteurization,  by  destroying 
the  lactic-acid  bacteria,  allows  the  development  of  other  less  desirable 
bacteria,  which,  without  aflfecting  the  taste  of  the  milk,  make  it  actu- 
ally dangerous,  especially  as  a  food  for  young  children. 


BACTERIA    OF    PA8TEURIZP:D    AND    UNPASTEURIZED    MILK.       31 

It  is  well  established,  however,  that  under  eertaiii  circunistances 
the  intestinal  troubles  of  children  nuiy  be  reduced  l)y  pasteurization 
of  the  milk. 

The  experimental  work  may  be  summarized  as  follows: 

Milk  was  pasteurized  under  laborator}'  conditions  in  a  continuous 
machine  at  85^  C.  (185'^  F.),  the  bacteria  being  reduced  from  over 
10,000,000  per  cubic  centimeter  to  less  than  500  per  cubic  centimeter. 

J////'  held  at  W^  V.   {68^  F.).—h\   the  unhealed   milk  the  lactic, 
bacteria  increased  rapidly  and  the  milk  became  acid  in  about  12  hours. 
The  peptonizing^  bai-teria  increased  in  ♦!  houi's  to  about  5,000.0(K)  per 
cubi<'  centimeter  and  then  decreased  slowly. 

In  the  heated  milk  the  j)eptonizinji-  bacteria  increased  rapidly  after 
12  hours,  and  tlu>  milk  was  usually  curdled  in  4.S  houi's,  with  a  disajiree- 
able  taste  and  odor.  Occasionally  lactic  bacteria  survived  pasteuriza- 
tion and  nndtiplied  rapidly  after  24  hours,  completely  inhil)itintr  the 
peptonizing  bacteria. 

MUl-  held  at  10-  C.  {50-  F.).--l\\  unheated  milk  the  growth  of  the 
bactei"ia  and  the  conseijuent  curdling  of  the  milk  was  nnich  I'etarded. 
The  average  milk  did  not  contain  sutHcient  acid  to  affect  t\w  taste 
until  it  was  over  4<S  hours  old.  The  proportion  of  peptonizing  to 
lactic  bacteria  was  greater  than  at  the  higher  temperature,  and  the 
taste  of  the  milk  occasionally  showed  the  influence  of  the  formcM-. 

In  the  pasteurized  milk  tiie  l)acteria  increased  very  slowly,  and  in 
nearly  every  case  the  milk  was  unchanged  in  taste  and  apj)earance  IH) 
hours  after  pasteuiMzation.  In  only  2  of  14  cas(>s  was  thei-e  a  marked 
increase  of  peptonizing  l)acteria.  The  predominating  t>act(MMa  weiv 
species  having  little  or  no  effect  on  milk. 

The  lactic  bacteria  inliibit(>(l  the  development  of  the  jx'ptonizing 
bacteria  oidy  when  tlicy  had  devclojx'd  sullicicMit  acid  to  render  the 
milk  unfit  for  use. 

It  seems  probaltle  that  the  acid  had  a  distinct  iiihit)itoi'v  action  on 
the  j)roteolyti(!  enzymes  of  the  peptonizing  l)acteria. 


Hiiu.nxih'Ai'in  . 

( 1 )  WniTAKKFj,  ( Ji:<).  !M. 

Tlif  milk  sii|>]ily  of  lloston  ami  ullicr  New    l'!iii:l:iii<l  citit's.      I".  S.  I  )f|>artiiu'iil 
uf  Airriciiltutv.  I?nrcan  nl  Animal   Imhistrv,  I'.iil.  •_'(».      Wash.,  ISitS. 

{'!)■  Wahd,   la)\\  aui>  <  i.,  .In. 

Milk  traii.^portatiuii.      I'.  S.  I  )f|)attm<'iit  nl    .\irri('iiitiirf.  Oivisidii  nt'  Statistics, 
liiil.  L'.">.      Wasli..  I!t(i;;. 

('^)  SKixavH  K,  \V.  T..  and  IV\  iciiki.dkh,  .Inns    I,. 

.V   hactfriolonical  cxaiiiiiiafii'ii   cif    tin-    lioston    milk  supiily.      jinst.  Mctl.  ami 
Siiri:.  .Irn..  v.  I'Jti.  N...  •_>,  |,|..  •_'.")  -js.      Kostnti.  .Ian.   14.  lsii-_'. 

(4)    llii.i.,  II.  W.,  and  Siac  k,  V.  II. 

Bacterial  coiiiit.'^  uf  Boston's  milk  snpi'lv.      .\m.  .Irn.  Biili.  Hv^'.  ami  .Irn.  Mass. 
A.syoL'.  Boanl.s  of  Ih-alth,  v.  14.  No.  4,  pji.  1.':{(>-24S.      Bost<m.  Nov..  lUtM. 


32  BUREAU    OF    ANIMAL    INDUSTRY. 

(5)  Park,  W.  H. 

The  great  bacterial  confamination  of  the  milk  of  cities.  Can  it  be  lessened 
by  the  action  of  health  authorities?  Jrn.  of  Hyg.,  v.  1,  No.  3,  pp.  391-406. 
Cambridge,  July,  1901. 

(6)  Bergby,  D.  H. 

Sanitary  supervision  of  the  collection  and  marketing  of  milk.  Univ.  of  Penn- 
sylvania Med.  Bui.,  V.  17,  No.  5-6,  pp.  187-192.     Phila.,  July-Aug.,  1904. 

(7)  P.\RK,  W.  H.,  and  Holt,  L.  E. 

Report  upon  the  results  with  different  kinds  of  pure  and  impure  milk  in  infant 
feeding  in  tenement  houses  and  institutions  in  New  York  City.  A  chemical 
and  bacteriological  studv.  Med.  News,  v.  83,  No.  23,  pp.  1066-1078.  N.  Y., 
Dec.  5,  1903. 

(8)  .\lvord,  Henry  E.,  and  Pearson,  R.  A. 

The  milk  supply  of  two  hundred  cities  and  towns.  U.  S.  Department  of 
Agriculture,  Bureau  of  Animal  Industry,  Bui.  46.     Wash.,  1903. 

(9)  Smith,  Theobald. 

The  thermal  death  point  of  tubercle  bacilli  in  milk  and  some  other  fluids. 
Jrn.  of  Exper.  Med.,  v.  4,  No.  2,  pp.  217-233.     N.  Y.,  March,  1899. 

(10)  RossELL,  H.  L.,  and  Hastings,  E.  G. 

The  thermal  death  point  of  tubercle  bacilli  under  commercial  conditions. 
Wis.  Agr.  Exp.  Sta.,  17th  Ann.  Rept.  for  year  ending  June  30,  1900,  pp. 
147-170.     Madison,  1900. 

(11)  Harding,  H.  A.,  and  Rogers,  L.  A. 

The  efficiency  of  a  continuous  pasteurizer  at  different  temperatures.  N.  Y. 
Agr.  Exp.  Sta.,  Bui.  172,  pp.  507-530.     Geneva,  Dec,  1899. 

(12)  Bang. 

Some  experiments  on  the  temperature  necessary  for  killing  tubercle  bacilli  in 
milk.  Trans,  of  the  Brit.  Cong,  on  Tuberculosis  for  the  Prevention  of 
Consumption,  Lond.,  July  22-26,  1901,  v.  3,  pp.  392-398.     Lond.,  1902. 

(13)  Russell,  H.  L.,  and  Hastings,  E.  G. 

Effect  of  short  ])eriods  of  exposure  to  heat  on  tubercle  bacilli  in  milk.  Wis. 
Agr.  Exp.  Sta.,  21st  Ann.  Rept.  for  year  ending  June  30,  1904,  pp.  178-192. 
Madison,  1904. 

(14)  Variot,  G. 

Valeur  nutritive  du  lait  de  vache  sterilise  a  108°  pour  Tallaitement  artificiel. 
Compt.  Rend.  Acad,  des  Sci.,  t.  139,  No.  23,  pp.  1002-1003.  Paris,  Dec.  5, 
1904. 

(15)  Conn,  H.  W.,  and  Esten,  W.  M. 

The  effect  of  different  temperatures  in  determining  the  species  of  bacteria 
which  grow  in  n)ilk.  Storrs  Agr.  Exp.  Sta.,  16th  Ann.  Rept.  for  year  end- 
ing June  30,  1904.     pp.  27-88.     Middletown,  Conn.,  1904. 

(16)  FLt:GGE,  C. 

Die  Aufgaben  und  Leistungen  der  Milch-Sterilisirung  gegenuber  den  Darm- 
Krankheiten  der  Siiuglinge.  Ztschr.  f.  Hyg.  u.  Infekt.,  Bd.  17,  Hft.  2,  pp. 
272-.342.     Leipz.,  1894. 

(17)  Weber,  A. 

Die  Bakterien  der  sogenanten  sterilisierten  Milch  des  Handels,  ihre  bio- 
logischen  Eigenschaften  und  ihre  Beziehungen  zu  den  Magendannkrank- 
heiten  der  Siiuglinge,  etc.  Arbeiten  aus  dein  kaiserlichen  Gesundheit.«amte, 
Bd.  17,  Hft.  1,  p.  108-1.55.     Beriin,  1900. 

(18)  LtJBBERT,   A. 

Ueber  die  Natur  der  Giftwirkung  peptonisirender  Bakterien  der  Milch. 
Ztschr.  f.  Hyg.  u.  Infekt.,  Bd.  22,  Hft.  1,  pp.  1-11.     Leipz.,  June  25,  1896. 

(19)  CoHN,  Ferdinand. 

t^ber  Bakterien,  die  klein.«ten  lebenden  Wesen.  47  p.  17  cm.  New  York, 
Henry  Holt  &  Co.,  1889. 

(20)  BorsKA.  F.  W. 

fctudes  sur  rantagonisme  entre  les  V)actcries  dn  groupe  des  feriiient»<  lactiques 
et  celles  du  groupe  du  Bacillus  subtiiis.  Hev.  g6n.  du  lait.  v.  3,  No.  1, 
pp.  1-11.     Oct.  15,  1903. 

O 


REGIONAL  LIBRARY  FACIUTV 


(Continued  from  second  page  of 


001  083  172 


Dr.  E.  (;.  .Foss,  care  Carstcns  Packing  Co.,  Taco^ 
,  ma,  Wash. 
Dr.  J.  S.  Kelly,  care    Blomcr  &  Michael  Co., 

Qiiiiicy,  111. 
Dr.  F.  D.  Ketchum,  South  St.  Paul,  Minn. 
Dr.  A.  Long,  care  Sperry  &  Barnes,  New  Haven' 

Conn. 
Dr.C.  Lovcberry,  room  402, Custom-House  (new), 

Portland,  Oreg. 
Dr.  H.  D.  Mavne,  Malone.  N.  Y. 
Dr.-r>oui.s  .Met-sker,  rcmm  22,  N.  T.  Armijo  Build- 
ing, Albuquerque,  N.  Mex. 
Dr.  J.  Miller,  care  John  Morrell  &  Co.,  Ottnmwa. 

Iowa. 
Dr.  C.  L.  Morin,  St.  Alban.s,  Vt. 
Dr.  W.  J.  Murphy,  care  Springfield  Provision  Co., 

Brightwood,  Ma.s.s. 
Dr.  W.  N.  Neil,  care  John  Cudahy  Co.,  Wichita, 

Kanfi. 
Dr.  V.  A.  Norgaard,  Honolulu,  Hawaii. 
Dr.  F.  M.  Perry,  Fort  Fairfield,  Me. 
Dr.  <i.   W.   Pope,  Animal    Quarantine   Station, 

Athenia,  N.  J. 
Dr.  H.  T.  Potter,  Calais,  Me. 
Dr.  J.  O.F.Price,  care  Brittain  &  Co.,Mar.-hall- 

town,  Iowa. 


Dr.  R.  A.  RauLsay,  Fargo,  N.  Dak. 

Dr.  A.  G.  G.  Richardson,  707  Empire  Building, 

Knoxvllle.  Tenu. 
Dr.  A.  E.  Righel,  cure  Cudahy  Packing  Co.,  Los 

Angele.s,  Cal. 
Dr.  W.  H.  Rose,  18  Broadway,  New  York,  N.  Y. 
Dr.  F.  L.  Ru.ssell,  Orono,  Me. 
Dr.  J.  F.  Ryder,  141  Milk  st.,  Boston,  Mass. 
Dr.  K.  P.  SchafTter,  care  Cleveland  Provision  Co., 

Cleveland,  Ohio. 
Dr.  C.  A.  Schaufler,  134  South  Second  st.,  Phila- 
delphia, Pa. 
Dr.  Th(j8.  W.  Scott,  care  The  Rath  Packing  Co., 

Waterloo,  Iowa. 
Dr.T.  A.  .Shipley,  care  T.  M.Sinclair  &  Co.  (Ltd.), 

Cedar  Rapids,  Iowa. 
Dr.  N.  C.  Sorensen,  care  Kingan  &  Co.,  Indian- 

apolLs,  Ind.  ~ 

Mr.  Wni.  H.  Wade,  Animal  Quarantine  Station, 

Halethorp,  Md. 
Dr.  H.  N.  Waller,  109  West  42(1  st.,  New  York,  N.  Y. 
Dr.  G.  W.  Ward,  Newport,  Vt. 
Dr.  B.  P.  Wende,  Live  Stock  E.vchange  Building, 

East  Buffalo,  N.  Y. 
Dr.  W.  H.  Wray,34  Streatham  Hill,  London,  S.W., 

England. 


University  of  California 

SOUTHERN  REGIONAL  LIBRARY  FACILITY 

405  Hilgard  Avenue,  Los  Angeles,  CA  90024-1388 

Return  this  material  to  the  library 

from  which  it  was  borrowed. 


REC'O  LO  u 


J^N  1 .3  laUb 


University  ( 
Southern 
Library 


